Melt the butter and chocolate in a saucepan (or directly in the Omnia pan)
Combine the sugar, flour and baking powder in a bowl. Add the melted butter, chocolate and vanilla. Stir into a smooth batter. Add one egg at a time and stir until smooth.
Pour the batter into the pan (preferably use the silicone mold, but if you do not have one, grease and flour the pan first). Bake at low heat for about 20 minutes. Test for doneness with a toothpick (there should be no wet batter). If necessary, bake for a minute or two more.