Coffee and chocolate crumble tart

A lovely tart, crisp outside and creamy inside. Very quick by hand or processor with no pastry rolling. Make the day before and refrigerate for improved flavour.
INGREDIENTS FOR A 22/24 CM TIN
BASE
300 G ITALIAN 00 FLOUR
30 G UNSWEETENED COCOA
100 G TOASTED, CHOPPED HAZELNUTS
2 MEDIUM EGGS
150 G CASTER SUGAR
120 G BUTTER
8 G BAKING POWDER
1 PINCH SALT
VANILLA POWDER OR PODI first make custard and chill.
COFFEE CUSTARD INGREDIENTS
400 ML WHOLE MILK
80 ML STRONG COFFEE
1 HEAPED TEASPOON INSTANT COFFEE, or increase strong coffee to 100 ml
4 EGG YOLKS
160 G SUGAR
50 G ITALIAN 00 FLOUR OR CORNFLOUR
80 G DARK CHOCOLATE CHIPS
I boil milk and add strong and instant coffee. I mix yolks and sugar in a bowl.I whisk and add cornflour.I mix without lumps and gradually whisk in boiling milk. I heat in a small saucepan until thickened, stirring well.I transfer to a bowl, cover directly with cling film and refrigerate when cold. BASE
While custard cools, I put flour, sugar and salt in a processor, or bowl for hand mixing.I add cocoa and baking powder.I add vanilla powder, butter and eggs.I process briefly and add hazelnuts, not finely chopped because I like their texture.I briefly process into crumbs.I line tin base with parchment and press in half the mixture. I add cold custard, leaving edges free.I scatter chocolate chips, reserving a tablespoon.I mix reserved chips with remaining crumbs and fully cover custard.I bake at 180°C for 45 minutes, cool completely, unmould and refrigerate, even for a whole day. I remove 15 minutes before eating. From the Ho voglia di dolce blog, which I thank.