Filling of your choice. (Optional)
Grease a square microwaveable dish. (I used a tupperware container.) Make sure it fits in the microwave.
Add 100g butter and about 75g brown sugar to a separate microwaveable bowl. (I had no scales so had to estimate.)
Microwave for 20 seconds, take out and stir, repeat until the butter and sugar are melted.
Add two tbsps of golden syrup to the butter and sugar and mix well.
Add about 200g of porridge oats and any fillings you would like. I used apricot, but you can use nuts, chocolate, oreos, other fruits, sweets - anything!
Mix the oats and flapjack filling together very well.
Tip the mixture into the greased dish and use a spoon to press the mixture down well.
Microwave the mixture for five minutes.
When it comes out of the microwave it will look really soft and gooey, but leave it to cool for an hour or so and then you can tip it out of the dish and cut into squares/bars.
You can also top with melted chocolate etc if you wish.