01 -
Start by tossing the flour, cocoa, powdered sugar, and a pinch of salt together in a bowl. Rub in the cold butter using your hands or a pastry blender till you get a crumbly texture. Add in the egg yolk. Pour in a splash of cold milk, little by little, just till the dough sticks together. Shape it into a disc, cover it up, and pop in the fridge for half an hour minimum.
02 -
Fire up the oven to 350°F (175°C). Roll out your chilled dough, set it in a 9-inch tart pan, and trim off the edges. Prick the bottom with a fork. Cover with parchment. Fill with dry beans or pie weights. Bake 15 minutes, take out the beans and paper, and keep baking 10 more minutes. Let your crust cool down all the way before moving on.
03 -
Warm up the heavy cream till it's just bubbling. Throw that hot cream over your dark chocolate in a fresh bowl and let them sit undisturbed for a couple minutes. Stir until you have a sleek chocolate mix. Swirl in vanilla and a pinch of salt. Pour this ganache in the cooled tart shell, then chill it till firm—about 30 minutes.
04 -
Throw pistachios and milk in a blender and blitz till smooth. Scoop that out into a pot. Now add heavy cream, sugar, and your cornstarch. Stir over medium heat until it turns thick like pudding. Take it off the burner, mix in almond extract if you like, and cool for a few minutes. Toss in a handful of roasted pistachios. Spread this layer over the firm ganache and set it in the fridge for 30 to 45 minutes.
05 -
Get your heavy cream hot, dump it over chopped chocolate and butter in a bowl. Stir it all together till the chocolate is shiny and smooth. Carefully pour this over the set pistachio cream and smooth it out with a spatula.
06 -
Scatter whole or chopped roasted pistachios around the edges for a good look. Stick the whole tart in the fridge for at least an hour before you slice—this really helps keep those layers crisp.