In a mixer with a paddle attachment, cream the butter until fluffy. Add 1/2 cup of the sugar and cream together until light and fluffy. Add the flour, cornstarch, and pepper, and mix just until combined. On a well-floured surface, roll out the dough to about 3/4-inch thickness. Transfer it to a parchment paper-lined baking sheet (preferably one with sides) and continue rolling out the dough, pushing out towards the edges of the pan, to 1/4-inch thickness. Prick the dough all over with a fork, then sprinkle with 1 tablespoon sugar.
Bake for 25 to 30 minutes, rotating the pan after 10 minutes. Shake the pan as you rotate it, to settle the dough. When the surface is golden, remove from the oven and sprinkle immediately with the remaining 1 tablespoon of sugar. Cut immediately into bars with a sharp knife or pizza cutter and let cool in the pan. Store in an airtight container.