16 tablespoons (2 sticks/226 grams) unsalted butter, softened
1/2 cup (113 grams) granulated sugar
1 2/3 cups (226 grams) all-purpose flour
1/2 cup (113 grams) semolina
2 tablespoons demerara sugar
Preheat the oven to 325 degrees with a rack in the middle position. Have ready a 9-by-13 baking pan.
In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter and sugar on low speed just until combined. (You’re only looking to incorporate them, not add a lot of air to the mixture.) Alternately, you can use a handheld mixer or even a wooden spoon in a large bowl. Stir in the flour and semolina on low speed until combined. The dough won’t come together into a cohesive mass, so don’t be surprised if it’s crumbly. Clumps, however, should form when pressed together between your fingers. You can briefly knead the dough by hand, if needed.
Press the mixture into the pan, level and smooth the top using the bottom of a dry measuring cup or the back of a spoon. Sprinkle with the demerara sugar, and bake for about 30 to 35 minutes until pale golden brown.
Remove from the oven and let the pan cool on a wire rack for 5 minutes. With the tip of a sharp knife, score the slab to form 24 triangles (we accomplished this with three rows of four squares that we then cut in half). Let the shortbread cool completely in the pan before lifting the pieces out.
Note: Mary Berry mixes the all-purpose flour with semolina, a coarse flour you often find in pizza or pasta, for extra crunch. For an even more melt-away mouthfeel, swap in equal amounts of cornstarch or rice flour for the semolina. Prefer only flour? That’s fine, too. Whatever you use, be sure not to overwork the mixture, as it will create too much gluten and toughen the dough.
Make Ahead: The shortbread will keep in an airtight container at room temperature for up to 2 weeks.