Preheat the oven to 390°F / 200°C and grease a Ø 24 cm round springform pan with butter and line the bottom with parchment paper.
NOTE: You can also use the oven’s fan-force at 360°F / 180°C as it will make a more crispy and caramelized crumble topping. Keep an eye on it though to make sure it doesn’t brown too much.
Whisk the flour, sugar, and baking powder together in a large mixing bowl until combined. Cut the butter into dry mixture until it resembles coarse crumbs.
TIP: I like to pop the butter in the freezer until it’s hard and then grate the frozen butter through the large holes of a box grater directly into the dry ingredients and then let my fingertips do the rest of the work. Alternatively, use two knives (or a pastry blender) to cut the butter into the flour until you have little tiny bits of butter. Then take over and crumb the mixture by rubbing it together with your fingers.
Sprinkle about 1/2 of the crumble mixture over the bottom of the prepared spring form pan. Press it down and up the sides of the pan. Transfer to the preheated oven and bake for about 5-6 minutes (pre-baking is optional, but helps avoid a soggy base.
IMPORTANT: keep an eye on it, as it browns quite quickly).