These delicious bars will keep at room temperature for a few days in an airtight container, although they probably wont last that long!
Preheat the oven to 375 degrees F. Butter a 9×13 inch pan.
In a medium bowl, mix together 1 cup sugar, flour, and baking powder. Add in salt and lemon zest. Use a fork or pastry blender to incorporate the butter and egg. The dough will be crumbly. Pat half of the dough evenly into the buttered pan, and set aside the rest.
Spread the jam evenly over the dough in the pan. Crumble remaining dough over the jam. Bake for 40-45 minutes, or until top is a light golden brown. Cool completely before cutting into bars.