Chocolate brownies keep well and, in fact, are better left for a while.
Also Nigella's Dense chocolate loaf cake keeps really well.
225g soft butter
375g dark muscovado sugar
2 large eggs
vanilla extract
100g dark chocolate
200g plain flour
1 tsp bicarb
250 ml boiling water
Oven Gas mark 5, 190C
Cream the butter and sugar, then add the eggs and some vanilla essence. Melt the chocolate, and fold it into the mixture. Mix the bicarb with the flour, then add it to your mix, spoon by spoon, alternating with the boiling water. The result should be a smooth batter. Pour it into three 1-lb loaf tins, and bake for 30 minutes at 190C. The cake should be squidgy in the middle, so you can?t test it with a skewer.
As it cools it will sink in the middle, sometimes to the point of total collapse. It improves with keeping.
I change the recipe slightly and make it with 300g sugar and do half dark and half light muscovado.