Beat 250 g of soft butter until foamy.

Gradually mix in 150 g of sugar and the eggs until light and airy.

In another bowl, combine 400 g of wheat flour with the baking powder and a pinch of salt; mix in the grated lemon zest.

Alternate stirring the flour mixture into the butter mixture with the milk until combined.

Spread the dough onto a greased and floured baking sheet.

Preheat oven to 180°C (or 160°C for convection).

Clean, wash, and chop the rhubarb into manageable pieces.

Toss the chopped rhubarb with vanilla sugar and sugar.

Knead together flour, 100 g of butter, 50 g of sugar, and chopped almonds to create the crumble.

Layer the rhubarb mixture over the dough.

Sprinkle the crumble on top.

Bake in the preheated oven for about 45 minutes until golden brown.

Let it cool, and dust with powdered sugar if desired before serving.