Prepare a half sheet tray, or two quarter sheet trays, by buttering and lining with parchment paper. Allow a two-inch overhang on the long sides of the pan to help release the shortbread later after they have been baked.

Cream butter and sugars in a stand mixer with the paddle attachment until light and fluffy. Add eggs and vanilla until combined, then mix in dry ingredients. Combine completely.

Divide dough evenly into prepared sheet trays, spreading smooth and level. The dough is sticky, so I found it easier to work with by keeping my hands wet while pressing the dough into the pan. Sprinkle with granulated sugar and bake at 325° until golden brown, about 35 to 45 minutes.

Let cool completely before using a sharp knife to cut into squares. These keep well at room temperature for at least a week!