In a small bowl sift in the cornstarch add the water and stir until smooth.
In a small pot add the jam and heat on low for 1 minute, add the cornstarch mixture, stir to combine, continue to cook on low stirring constantly until thickened approximately 2-4 minutes, move to a small bowl, let cool, cover and chill for 1 hour.
Pre-heat oven to 350F/180C. Line an 8 inch / 20 cm square pan with parchment paper.
In the stand mixer beat the butter and sugar for 2-3 minutes or until creamy, add the egg and vanilla, beat until smooth, add the flour and salt, beat just to combine.
Divide the dough in half, place one part on the bottom of the prepared pan, spread evenly with the jam filling, crumble the remaining dough on top of the jam.
Bake until golden approximately 40-45 minutes, let cool in the pan 10-15 minutes, then move to a wire rack to cool completely. Dust with powdered sugar before cutting into squares and serving. Enjoy!
Notes
How to store the raspberry crumb bars?
Keep the cooled bars in an airtight container at room temperature up to 4-5 days, or refrigerate up to a week. If stacking, place parchment between layers so the crumble topping doesn’t stick. Or freeze the sliced bars on a baking sheet until firm, then transfer to a freezer-safe container or bag with parchment between layers. They keep well for up to 2 months. Thaw at room temperature before serving.