Place strawberries and sugar in a large skillet. Stir until combined and allow the mixture to sit for 10 minutes to allow some of the liquid to release from the berries. Add the lemon juice.
Turn the heat to medium and allow the mixture to come to a simmer, stirring frequently. The skillet will fill with liquid as it releases from the strawberries. Continue stirring until most of the liquid has evaporated or thickened up. This may take anywhere from 15-30 minutes. Once the jam is thick, remove it from the heat. It will continue to thicken as it cools.
Spray the inside of a 9x9 inch pan with baking spray and line it with parchment, allowing the paper to hang over two sides of the pan.
Cream the butter, powdered sugar and salt in a stand mixer on medium-high until light and fluffy. Add the vanilla, lower the speed and gradually add the flour until the dough is smooth. Briefly stir to ensure the dough is evenly combined.
Using plastic wrap, press the dough evenly into the prepared pan. Refrigerate for 30 minutes or overnight.
Preheat the oven to 350 degrees F. Bake the shortbread for 25-30 minutes, or until lightly golden on top. Allow to cool to room temperature.
To prepare the topping, combine the flour, brown sugar, almonds, salt and butter in a small bowl. Use a fork to mash the ingredients together until crumbly.
Spread 1 1/2 cups of the strawberry jam on top of the shortbread. Sprinkle the crumb topping over the jam.
Bake for 20-25 minutes, until the topping is brown. Allow to cool completely before slicing into bars.