Preheat oven to 350Line an 8-inch square pan with aluminum foil and cooking spray.
In a large bowl, add melted butter, sugars, vanilla, and whisk to combine.
Add the flour, oats, optional salt, and stir to combine.
Set 1 cup of mixture aside for the crumble topping.
Put the remaining mixture in the prepared pan. Pack the mixture to create an even, flat crust.
Evenly spread the raspberry preserves over the crust. Preserves should be 1/8-inch to 1/4-inch thick.
Sprinkle the 1 cup of crumble topping mixture onto the preserves.
Bake for about 30 to 32 minutes or until edges are set and it is lightly golden browned.
Allow to cool before serving.