Preheat the oven to 350°F (180°C). Line a brownie tin with baking paper letting the edges hang over the edge.
Put the chocolate and butter in a microwave-safe bowl and heat for 30 second bursts, stirring in between, until melted. Alternatively you can use the double boiler method: place the bowl over a saucepan of barely simmering water and the chocolate and butter to melt gradually.
Place the sugar, orange zest and eggs in a large bowl and use a hand whisk to mix together until frothy. Stir in the mincemeat if using.
Stir in the melted chocolate/butter mixture until thoroughly combined.
Sift in the flour, cocoa powder, salt and spices and stir to combine. You should have a glossy thick batter.
Bake for 30 minutes until the edges are set but the middle is still a little squidgy.
Allow the brownies to cool before cutting.
Remove the brownies from the tin using the paper lining to lift them out. Cut into triangle shapes.
If you are decorating them, mix the icing sugar, vanilla extract, green food coloring and enough milk to make a pourable icing.
Drizzle over the brownies and add sprinkles or decorations while the glaze is still wet.
You can add chocolate ‘fingers’ to create the tree trunks and little gingerbread stars to top if you like.
Video
Notes
If you don't like mincemeat (or can't find any) you could add (equal weight) chopped mixed citrus peel, chopped nuts or dried fruit instead.