From mrsmikey-simmo:
500g oats
300g butter
4 serving spoons golden syrup
340g Demerara sugar
1/2 tin condensed milk
Melt butter in pan, add sugar and heat gently until sugar mostly dissolved but take care not to let it boil. Add golden syrup and condensed milk and stir well to mix then add oats. Don’t add so many oats that it becomes dry. Line large tin with baking paper and put mixture in to a depth of ~2-3 cm. bake at 180 deg C for about 15-20 mins until slightly brown around the edges. Don’t over bake or they will be too hard. The other thing you can do is to slice up some cooking apples thinly and microwave with a generous sprinkle of cinnamon then put half flapjack in tin, lay apple slices on top then cover with rest of flapjack mix.
This recipe makes a lot and they are seriously calorific but cut into small squares and pop in freezer then take one out as and when so that you don’t scoff the lot in one go. Use bits of grease proof paper to separate layers of flapjack pieces in the tub so they come out individually rather than one lump!