Adjust an oven rack to the center position and preheat the oven to 300 degrees.
Have ready an ungreased 9-inch ovenproof pie plate.
To measure the all-purpose flour, dip dry measures into the flour container, fill to overflowing, and level off.
To measure the rice flour, set dry measures on a piece of waxed paper, pour the flour into them to overflowing, and sweep off excess.
Combine both flours, sugar, and salt in the mixer bowl. Add the butter pieces and attach the flat beater.
Mix on low speed until the dough forms large clumps that look as though they’ll gather into a single mass. This can take as long as 10 minutes!
Squeeze all the pieces together to form one coherent mass.
Press evenly into the pie plate and prick all over with a fork. I’m told this helps the shortbread cook evenly.
Bake 60 to 70 minutes, or until the shortbread is an even pale sandy color. It should not be darker than a very pale brown. The edge of the shortbread may be slightly raised. The center will seem soft. The fork marks will have disappeared.
Cool for 30 minutes on a wire rack, then use a paring knife to release shortbread from sides of pan and cut the cookie into 16 wedges.
Cool for 30 minutes on a wire rack, then use a paring knife to release shortbread from sides of pan and cut the cookie into 16 wedges.
Cool completely before removing wedges from the pan. Store airtight. Shortbreads will stay fresh for at least a week. They get crunchier over time.
