In a stand mixer fitted with the paddle attachment, beat the butter and sugar together on medium speed until smooth and combined, about 2 minutes. Do not overmix. You want it creamy, not whipped.

Reduce speed to low and gradually add the flour, rice flour, and salt. Mix just until a soft, sandy dough forms and begins to clump together.

Press the dough evenly into a 9x9 baking pan lined with parchment paper, keeping the thickness close to ½ inch. Smooth the top with your hands or a flat spatula. Cover lightly with plastic wrap and chill for 30–45 minutes, or until firm.

Remove the plastic wrap. Use the tines of a fork, a skewer, or the tip of a toothpick to dock the dough in even rows. This helps steam escape and creates that classic shortbread pattern.

Bake the entire slab at 325°F for 30–35 minutes, or until the edges turn golden brown and the top looks dry and set. The center should remain pale.

Let the pan cool completely on a wire rack. Once fully cooled and set, lift the slab out using the parchment paper overhang. Transfer to a cutting board and use a sharp knife to cut into fingers, wedges, or squares. Press straight down for the cleanest edges.

Keep shortbread in an airtight container at room temperature for up to 1 week. For longer storage, freeze well-wrapped pieces for up to 2 months.