Mix together the flour, xanthan gum if using and cocoa powder, then add the butter cubes. Rub through and together with your fingertips until the mixture resembles breadcrumbs. Gradually add in the water, a tsp at a time, until the pastry just comes together. Form it into a ball, wrap in clingfilm and chill for 30 minutes. You can also use my separate gluten-free pastry recipe for this

Preheat the oven to gas 5 / 190C / 375°F. Roll out the pastry fairly thinly on a floured surface. Cut out 10cm circles with a cutter and gently press into the holes of a muffin tin or if you have them, individual flan cases. Prick the bottom of each pie with a fork and then line each pie with a crumpled square of baking paper. Fill with baking beans and bake for 10 minutes, then remove from the oven and take out the baking beans and paper. Return to the oven for 2-3 minutes to ensure you don't get a soggy bottom!

Let the pastry cool in the moulds for a few minutes before tipping out. Let them finish cooling on a wire rack. Make the chocolate mousse as per my other recipe. Fill each pastry case halfway with the mousse, then refrigerate for at least 3 hours. Make the ganache before you take the pies out of the fridge

Chop the chocolate quite small. Heat the cream in a saucepan and when almost boiling, take off the heat and stir in the chocolate until the mixture is thick and smooth. Let cool enough so it's still spreadable but not warm enough to melt the mousse. Spoon on top of the mousse and smooth out

At this stage I like to just sprinkle with chocolate strands or powdered sugar but it's also nice to put a dollop of chantilly cream on top and decorate with chocolate curls

You can also change the base to suit yourself. A biscuit like oreos or bourbon creams mixed with some melted butter make a nice base, or you could go raw and make one from pecan or hazelnuts which is delicious

If the thought of the avocado mousse scares you too much (be brave, you'll thank me later) double the ganache instead. When almost cooled whip it up with a whisk and fill that into the pastry instead, then top with chocolate flavour icing instead