Preheat your oven to 300 degrees F. Line a 9” by 13” baking dish with parchment paper; allow a few inches of paper to hang over the sides, to allow for easy bar removal.
Next make your crust. Combine the melted butter with granulated sugar, vanilla extract, salt, and flour. Press this mixture into your lined dish, pressing (with clean hands) to ensure it is an even thickness throughout. Pre-bake this crust for 15 minutes.
While the crust is baking, make the streusel. Combine oats, brown sugar, cinnamon, and flour in a mixing bowl. Cube the butter into this mixture and combine using a pastry cutter. The streusel is ready once the texture is uniform.
Once the crust is done, remove from the oven and allow to cool briefly. Increase the oven temperature to 350 degrees F.
Cover the crust with raspberry jam. Place fresh raspberries across the surface of the preserves.
Spread streusel in an even layer over your raspberries.
Bake at 350 degrees F for 30-35 minutes, or until the streusel is just starting to turn golden brown. Allow to cool completely before removing from the pan.
While the bars are cooling, whisk together powdered sugar, vanilla bean paste, and 2 tablespoons of milk. Add additional milk until the icing reaches your preferred texture.
Once the bars have cooled completely, drizzle with vanilla icing before slicing and serving.
Store-bought vanilla icing is a perfectly acceptable substitution!