Place all of the filling ingredients EXCEPT for the raspberry preserves into a high-speed blender, and blend on high until smooth, scraping down the sides occasionally.
Spread the raspberry preserves over the baked shortbread crust, then gently pour the almond mixture over the preserves. Smooth the almond filling with the back of a large spoon taking care not to mix the preserves into it so the layers remain separate. Sprinkle the top with almond slices and bake for 30-40 minutes or until golden, turning half way through baking.
Let the tart cool completely before removing the sides of the tin. Dust with confections sugar, and serve.