Step 1

Preheat oven to 350F. Line an 8-inch square pan with aluminum foil and spray with cooking spray; set aside.

Step 2

To a large, microwave-safe bowl add the butter and heat on high power to melt, about 1 minute.

Step 3

Add the sugars, vanilla, and whisk to combine.

Step 4

Add the flour, oats, optional salt, and stir to combine. Mixture will have some larger, well-formed crumble pieces as well as some sandier, dryer bits.

Step 5

Set 1 heaping cup mixture aside to be sprinkled on later as crumble topping.

Step 6

Transfer remaining mixture to prepared pan, and using a spatula or your fingers, hard-pack the mixture to create an even, smooth, flat crust.

Step 7

Evenly spread the raspberry preserves over the crust making sure there’s complete coverage. Preserves should be about 1/8-inch to 1/4-inch thick.

Step 8

Evenly sprinkle with the reserved heaping 1 cup crumble topping mixture. Before sprinkling, I squeeze the mixture in my palm to encourage bigger crumble pieces to form.

Step 9

Bake for about 30 to 32 minutes, or until edges are set and center has just set and is lightly golden browned. Place pan on a wire rack and allow bars to cool for at least 2 hours before slicing and serving.