High-Calorie Flapjack Recipe: Energy Flapjacks That Actually Fuel You
A recipe from the team at Phoenix Bars. Last reviewed July 2026.
Quick answer: This high-calorie flapjack packs about 490 calories into each square, roughly double a shop-bought one, by building in nut butter, mixed nuts, dried fruit and dark chocolate on top of the usual oats, butter and syrup. It is made for energy, not dieting, so it suits hiking, long runs, expeditions and anyone trying to eat more calories than normal meals allow. The whole tray takes about 15 minutes of work plus baking, keeps for a week, and freezes for three months.
I'm James, I make Phoenix Bars, which are essentially a calorie-dense flapjack in a wrapper, and I have baked and eaten a frankly ridiculous number of test batches getting the balance right. Most flapjack recipes online are chasing "healthy," which usually means lower calorie. This one goes the other way on purpose. If your goal is fuel for the hills or putting weight on, a light flapjack is working against you, and the fix is denser ingredients, not a bigger portion you cannot finish. Here is the version I actually use.
How many calories are in a flapjack?
A shop-bought flapjack is usually around 250 to 350 calories. This high-calorie version is about 490 calories per square when you cut the tray into 12, or roughly 370 each if you cut 16 smaller ones. The whole tray comes to about 5,900 calories. That density, close to 5 calories per gram, is what makes it useful as trail or weight-gain fuel rather than a snack.
What makes a flapjack high in calories?
Fat and sugar density, in that order. Fat carries about 9 calories per gram, more than double carbohydrate or protein, so the single biggest lever is adding fat-rich ingredients: butter, nut butter and nuts. Sugars from syrup, brown sugar and dried fruit add fast-releasing energy and help it all bind. The oats give slow-release carbohydrate and the structure. Get those working together and you get a lot of calories into a small, chewable square without it tasting like eating a stick of butter.
Ingredients (makes 12 squares, about 490 calories each)
- 300g rolled or porridge oats, about 1,140 calories, for slow-release energy and structure
- 200g butter, about 1,470 calories, the main calorie-density and binder
- 150g golden syrup, about 450 calories, fast carbs and binding
- 100g soft brown sugar, about 380 calories, for chew and quick energy
- 150g smooth peanut butter, about 940 calories, calories plus a little protein
- 100g mixed nuts and seeds, roughly chopped, about 600 calories, for fat and crunch
- 100g raisins, or chopped dates or apricots, about 300 calories, quick sugars and moisture
- 100g dark chocolate chips, about 500 calories, for calories and palatability
- 2 tablespoons honey, optional, about 120 calories, extra binding and fast carbs
Method
- Heat your oven to 180C, or 160C fan, gas mark 4, and line a 20cm square tin with baking paper.
- In a large pan over low heat, gently melt the butter, syrup, sugar, peanut butter and honey together until smooth. Do not let it boil, just melt and combine.
- Take the pan off the heat and stir in the oats, nuts and seeds, and dried fruit until everything is fully coated.
- Let the mix cool for a couple of minutes, then fold in most of the chocolate chips so they hold their shape rather than melting away. Press the mixture firmly and evenly into the tin, and scatter the remaining chips on top.
- Bake for 20 to 25 minutes, until golden at the edges. The centre will still look soft, which is right, because it firms up as it cools.
- This next step is the one that matters. Cool the tray completely before cutting, ideally chilling it in the fridge for 30 minutes. Cutting flapjack while it is still warm is the main reason it crumbles. Once cold and set, cut into 12 squares.
Phoenix Bars: Up to 557 Calories Per Bar
Highly compact, low-volume, calorie-dense bars. Soft, easy to eat whole or as a warm porridge. Vegan, gluten-free and contain up to 66g of carbohydrates, 19g of protein & 8 vitamins & minerals.
How do you stop flapjacks falling apart?
Three things, and the third is the one most people skip. Use enough syrup and butter to bind, since a dry mix crumbles no matter what. Press the mixture down firmly in the tin so it sets as one slab. And cool it completely, ideally chilled, before you cut it. Warm flapjack has not set yet, so cutting it early is what turns squares into rubble.
Are flapjacks good for hiking and running?
Yes, which is why they are a classic endurance food. A good flapjack gives you fast carbs from the syrup and sugar for quick energy, slow carbs from the oats to sustain it, and fat for calorie density so you are not carrying much weight for the energy you get. Just as usefully, a proper flapjack does not melt into a mess in a warm pack or freeze rock solid in the cold the way a gel or a plain chocolate bar can, so it stays edible across conditions. Eat it in bites rather than all at once, and pair it with a few sips of water since it is dense.
Variations
To make it vegan, swap the butter for coconut oil or a vegan baking block, use maple or agave syrup in place of the honey, and use dairy-free chocolate. For a gluten-free version, use certified gluten-free oats, which is the only change needed. To make it nut-free, drop the peanut butter and nuts and add extra seeds like sunflower and pumpkin, plus a little more syrup or coconut oil to keep it binding. And to push the calories even higher, add more nut butter, stir in some desiccated coconut, or drizzle extra melted chocolate over the top once cooled.
If you would rather not bake
Baking a tray is the cheapest way to get calorie-dense flapjack, but it needs a kitchen, and it keeps for about a week. When that does not fit, for a multi-week expedition, a race drop bag, or just a busy week, our Phoenix Bars are the no-effort version of this exact idea: up to 557 calories each, soft and edible in the cold, a two-year shelf life so you can buy months ahead, and no crumbs to lose on the hill. You can also stir one into hot water to make porridge. For the homemade route in bar form rather than a tray, see our homemade high-calorie bars recipe.
Frequently asked questions
How many calories should a high-calorie flapjack have?
As a guide, aim for 400 to 500 calories a square if you want it as genuine energy or weight-gain fuel. This recipe lands around 490 per square, against 250 to 350 for a typical shop one.
Can you freeze flapjacks?
Yes. They freeze well for up to three months. Wrap them individually so you can grab one at a time, and they defrost in an hour at room temperature or overnight.
How long do homemade flapjacks keep?
About a week in an airtight container at room temperature. If you have made them richer with nut butter and dried fruit, they stay moist for several days rather than drying out.
Are these flapjacks healthy?
They are calorie-dense on purpose, so they are built for fuelling hard activity or gaining weight, not for cutting calories. Made from oats, nuts, seeds and dried fruit, they are wholesome, but they are energy food, so match them to that goal.
What is the best oat for flapjacks?
Rolled or porridge oats. Jumbo oats give a chunkier, looser texture, while standard rolled oats bind tighter and hold together better on the trail.
Related guides
Build the rest of your fuel from here: calorie-dense foods for the full ranking of what packs the most energy per gram, high-calorie snacks and best food for hiking for what else to carry, energy gel alternatives if you are moving away from gels, and how to gain weight if that is the goal.
About this recipe: I'm James, founder of Flaming Phoenix and Phoenix Bars, developed from more than 150 conversations with ultra-runners, expedition leaders and people who find it hard to eat enough. The bars are rated 5.0 out of 5 across more than 370 verified reviews. This recipe reflects that experience. It is general information, not medical or dietary advice. Last reviewed July 2026.
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