For the Crust:
1 1/2 cups all-purpose flour
3/4 teaspoon salt
10 tablespoons unsalted butter, chilled and cubed (1 1/4 sticks)
1/2 cup firmly packed light brown sugar
3/4 teaspoon vanilla extract
For the Streusel:
1/4 cup all-purpose flour
1/4 cup packed light brown sugar
1/4 cup rolled oats
1/4 cup chopped nuts, such as walnuts or hazelnuts
Dash ground cinnamon
4 tablespoons unsalted butter, cut into small cubes (1/2 stick) , chilled
3/4 cup seedless strawberry jam
Pre-heat the oven to 350ºF. Prepare an 8-inch by 8-inch baking dish by greasing it liberally with nonstick spray. Tear off a sheet of aluminum foil that is about 1 1/2x wider than the pan and press it down into the pan, letting the long edges overlap (this will make it easier to remove the bars from the pan later). Grease the foil with nonstick cooking spray and set the pan aside.
In a food processor, combine all of the ingredients for the crust and pulse until the mixture is combined (it will have the texture of sand). Turn the mixture out into the prepared baking dish and, using a small glass, press the dough into an even layer in the bottom of the pan (it will be crumbly). Chill the crust in the freezer for 10 minutes. Prepare the streusel by combining all of the ingredients in a medium mixing bowl. Using your fingers, rub the mixture together until the butter is worked into the flour and the streusel pieces are about the size of a pea. Set aside.
Remove the chilled crust from the freezer and carefully spread the jam over the crust, leaving a border of about 1/4-inch all the way around the edge. Sprinkle the streusel over the jam in an even layer. Bake the bars until the jam is bubbling and streusel is golden brown, 45 - 50 minutes. Cool completely. Using the foil overhang as a set of handles, lift the bars out of the pan and slice. Store the bars in an airtight container at room temperature for up to 5 days. NOTE: While this recipe uses strawberry jam, feel free to use whatever flavor you like.