Preheat your oven to 350°F (175°C) and line an 8x8-inch baking pan with aluminum foil, lightly spray with cooking spray.

Melt about ½ cup of butter in a microwave-safe bowl for approximately 1 minute, then whisk in ¾ cup granulated sugar, ¼ cup light brown sugar, and 1 teaspoon vanilla extract.

Add 1 cup all-purpose flour, 1 cup old-fashioned rolled oats, and a pinch of salt to the melted mixture. Stir until just combined and set aside a heaping cup for topping.

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

Spread 1 cup of raspberry preserves evenly over the crust, keeping it thin to avoid sogginess.

Sprinkle the reserved crumble mixture on top of the raspberry preserves and gently pat down.

Bake for about 30 minutes until the edges are set and lightly golden.

Cool completely on a wire rack for at least 2 hours before slicing.