Preheat your oven to 180 °C (fan) and line a baking tin with parchment paper. I used 25cm x 18cm, but anything around this size will work. Gather all your required ingredients.
In a small saucepan over low heat, melt the butter and honey together until smooth. Remove from heat and stir in the peanut butter and milk.
In a large mixing bowl, combine the oats, protein powder, chopped dates, chopped almonds, cinnamon, and salt. Mix well.
Pour the wet mixture over the dry ingredients. Mix thoroughly until all ingredients are evenly coated. The mixture should be sticky but manageable.
Transfer the mixture into the prepared baking tin. Press down firmly with a spatula or the back of a spoon to compact the mixture evenly.
Bake in the preheated oven for 20-25 minutes, or until the edges turn golden brown. The center may still feel slightly soft.
Remove from the oven and allow to cool in the tin for 10 minutes.
Lift the flapjack out using the parchment paper and place on a wire rack to cool completely.
Once cooled, cut into 12 bars (or desired number of pieces). Store in an airtight container at room temperature for up to 5 days, or in the fridge for up to 2 weeks.