Cook 500 g mulberries, 120 g granulated sugar, and 45 ml lemon juice over low heat for 30 minutes.

Blend the cooked mulberries coarsely, then simmer the jam for 5 more minutes until thickened.

Transfer the hot jam into sterilized glass jars, then let it cool completely.

Rub 300 g all-purpose flour, 150 g butter, 120 g powdered sugar, and 1 g salt together until sandy.

Add 1 egg and 1 egg yolk, then knead just until a smooth shortcrust dough forms.

Wrap the dough and chill it for 30 minutes.

Warm 500 ml whole milk with 15 g elderflowers and lemon zest, then steep for 10 minutes.

Strain the infused milk, then rewarm it over low heat.

Whisk 4 egg yolks, 100 g granulated sugar, and 40 g cornstarch until smooth.

Whisk the warm infused milk into the yolk mixture, then cook until the custard thickens.

Cover the custard and chill it until cold.

Roll out the chilled dough, then line one tart pan with it.

Spread the elderflower custard over the pastry, then spoon mulberry jam on top.

Bake the crostata at 180°C / 350°F for 35 minutes, then cool before slicing.