Preheat the oven to 180C/350F.

 Line an 20cm x 20cm (8inc x 8inch) square baking pan with non-stock baking paper.

To make the shortbread dough, place the flour, butter, sugar, and zest into a bowl of a food processor and pulse until the mixture forms a dough. It will be quite soft.

Lightly press the dough into the prepared baking pan and even out the surface. Bake for 20 minutes until starting to turn golden. Remove and allow to cool.

While the shortbread base is baking, melt the butter in a medium pot. Cook this until it starts to go golden brown then take it off the heat.

Add the sugars and allow to cool somewhat (it doesn’t not have to cool completely).

Add the egg one at a time giving the mixture a good whisk in between.

Add the vanilla, oats, raisins, and chocolate and give it a good mix.

Spread this mixture over the baked shortbread and sprinkle lightly with sea salt flakes (optional). Put the pan back into the oven and bake for a further for 20 minutes. It should be golden brown and set.

Allow to cool in the tin and then in the fridge to set further.