Add the flour, salt, sugar, baking powder, egg and milk to the food processor.

Use the hook to knead for 5 minutes at minimum speed, then continue kneading at 2nd speed until the dough has lifted from the sides of the bowl.

Add the cold butter and knead until fully incorporated into the dough.

Cover the dough with a tea towel and leave to rest at room temperature until doubled in volume, i.e. about 1? hours.

Meanwhile, prepare the streusel. Coarsely knead all ingredients to a lumpy paste, crumbling it with your fingertips. Refrigerate for 1 hour.

Once the dough has risen, fold over and shape into a ball. Roll out the dough in a round shape in a springform tin.

Brush the surface of the dough with a beaten egg.

Scatter the streusel over the surface.

Cover again with a dry kitchen towel and leave to rise at room temperature until the dough extends beyond the edge of the tin, about 1? hours.

Bake at 180°C for about 30 minutes.

Leave to cool when removed from the oven. Sprinkle with powdered sugar just before serving (optional).