Preheat oven to 350 degrees F. Line a 9x13 inch metal pan with non-stick foil. Lining it with foil makes the bars easier to lift and cut.

Beat the softened butter, sugar and salt (if using) together in a mixing bowl.

Mix together the flour and baking powder, then add flour mixture to butter mixture and stir until blended. Stir in the oats (or nut flour) to make a thick dough. Press ⅔ of the dough into the foil-lined pan.

Spread raspberry preserves over the dough, then crumble reserved dough over raspberry preserves.

Bake on center rack at 350 F. for 45-50 minutes.

Let cool completely, then cut into squares or bars.