For a light and flaky dough, cut butter into small pieces. Place in the freezer while you prepare the other ingredients. Mix flour, sugar and salt in a bowl. Work in the cold butter with your fingertips until it is coarsely crumbly.
Add egg yolk and cream, mix with a fork.
Pour the dough onto a lightly floured work surface and quickly form it into a slice so that the fat does not become too soft. Wrap in cling film and place in the refrigerator for about 2 hours. You can also freeze the dough for several months.
Bake the base blind: Preheat oven to 200 °C (electric oven). Roll out dough to 3 mm on a lightly floured work surface. Keep rolling pin and work surface floured so that the dough does not stick.
Work fast.
Place the dough in the mould, press down slightly on the sides and cut off the overhang to 5 mm. Shape the edge of the dough with your fingertips into a wavy shape. Prick sides and bottom with a fork. Place aluminium foil on the dough and weigh down with dry pulses.
This prevents the dough from shrinking or expanding during baking. Bake for 10 minutes, then remove aluminium foil and legumes, bake for another 8 minutes. Let it cool down.
Ganache: Put chopped chocolate in a bowl. Pour boiling cream over it. Stir with a whisk until the chocolate has dissolved. Spread over the base and chill.
Lemon filling: beat the egg, egg yolk and sugar together in a saucepan until the mixture becomes creamy and pale. Fold in lemon juice. Heat the egg yolk-sugar-lemon juice mixture over a low heat with a wooden spoon, stirring continuously, until it thickens at a temperature of 87°C.
Under no circumstances should the mixture boil, otherwise it will clot. Without letting it settle, whisk butter with a whisk piece by piece, followed by salt and lemon peel.
Allow to cool for 5 minutes before pouring the filling onto the chocolate tart. Before serving