Preheat your oven to 350°F (175°C) and prepare an 8x8-inch baking pan with foil or grease.

Melt 1/2 cup of butter in a microwave-safe bowl for about 1 minute until liquefied. Let it cool slightly.

Whisk 1/2 cup granulated sugar, 1/4 cup light brown sugar, and 1 tsp vanilla extract into the melted butter until glossy.

Add 1 cup all-purpose flour, 3/4 cup old-fashioned rolled oats, and a pinch of salt. Stir until combined and set aside 1 heaping cup for the crumble.

Press the remaining mixture evenly into the bottom of the prepared pan to form the crust.

Spread 1 cup raspberry preserves evenly over the crust, about 1/8 to 1/4 inch thick.

Sprinkle the reserved oat mixture over the raspberry layer. Squeeze some to create chunkier pieces for the crumble.

Bake in the preheated oven for approximately 30 minutes until edges are set and center is light golden.

Cool the baking pan at room temperature for at least 2 hours before slicing into squares.