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

Melt ½ cup of unsalted butter in a microwave-safe bowl for about 1 minute until completely smooth.

Combine melted butter with ½ cup granulated sugar and ½ cup light brown sugar; whisk in 1 teaspoon of vanilla extract until glossy.

Sift in 1 cup of all-purpose flour, 1 ½ cups of rolled oats, and a pinch of salt, mixing until just combined; reserve 1 heaping cup for topping.

Press remaining mixture into the bottom of the prepared pan evenly, aiming for a ¼-inch layer.

Spread 1 cup of raspberry preserves over the pressed oat mixture in an even layer.

Sprinkle reserved crumble mixture evenly over the raspberry preserves, pressing gently to ensure it adheres.

Bake for approximately 30 minutes until edges are set and center is lightly golden.

Cool in the pan on a wire rack for at least 2 hours before slicing.