Add all-purpose flour, sugar, brown sugar, and baking powder to a large bowl. Stir to combine. Add cold butter cubes. Using your fingertips, rub the butter into the flour mixture until there are no lumps or chunks of butter left. Add lemon zest and eggs. Stir to combine using a spatula, then knead with your hands until the dough comes together. Don't overwork it. It should remain crumbly. Press 2/3 of the crumble into the bottom of the baking dish (20 cm x 30 cm or 8-inch x 12-inch) lined with parchment paper. Keep the rest of the crumble dough chilled in a fridge. Preheat your oven to 190 °C / 370 °F.
Wash the raspberries and dry them. The easiest and fastest way to try them is to use a salad spinner. Place into a bowl and add powdered sugar, cornstarch, lemon juice, and raspberry liqueur (optional). Stir to combine well using a spatula. Spread the raspberry mixture over the crumble in the baking dish and sprinkle with the rest of the crumble dough.
bake and serve
Place the raspberry crumble to the preheated oven and bake for 35 - 40 minutes at 190 °C / 370 °F. Cool the baked raspberry crumble bars to room temperature then slice and serve. Enjoy. Store in an airtight container in a fridge for up to 3 days.