Line a baking tin 26x38cm (14.96 inches) with baking paper, if your tin is not deep use the baking paper to make a wall around the edge and staple into place. This prevents it overflowing in the oven.
Melt butter in the microwave, beat in sugar, eggs, cocoa and flour until just combined. Add the vanilla and marsala, pour into baking tray and sprinkle with chopped chocolate or nuts.
Bake at 180C (356 degrees Fahrenheit) until a knife inserted into the centre comes out clean