Preheat oven to 375 degrees F.
Prepare a 9 x 13 inch pan with butter or non-stick spray. Set aside.
Wash and peel peaches. Cut into slices about 3/8 to 1/2 inches thick. Set aside.
In a large bowl combine sugar, baking powder, flour, spices, and salt with a whisk, or an electric mixer on low speed.
Cut the butter slices into the flour mixture with a pastry blender, your fingertips, or a mixer.
Add the egg and continue to blend until crumbly. The mixture will look like sand with little chunks of butter.
Put 3 to 4 cups of the shortbread mixture into the prepared pan and pat down firmly.
Arrange sliced peaches in rows.
Sprinkle with remaining crust mixture.
Bake for 30 minutes or until it begins to brown around the edges.
Cool completely before cutting into squares.