This recipe is for the shortbread base only; it does not include fillings.
With a wooden spoon or electric hand mixer on low, cream ½ cup unsalted butter with ¼ cup granulated sugar until smooth.
Add Pinch of salt and sifted 1 cup all-purpose flour in two parts, combining well. Do not overmix. It will be crumbly.
Line an 8-inch square pan with aluminum foil or parchment paper and pat the dough evenly on the bottom. Lightly flour the tips of your fingers if needed to do this. Be sure all surface is covered as evenly as possible.
Prick the bottom with a fork and refrigerate for 30 minutes or freeze for 15 minutes.
Preheat the oven to 350ºF (180ºC).
Pre-bake for for 15 minutes, until starting to dry and color. Remove and reserve on a wire rack until you add the filling and bake it further. For no-bake fillings, bake the crust for about 25 minutes, until dry and fully baked. Let cool on a wire rack.
Notes
Baking time: consider that all ovens and pans are different, even if they look similar. The baking time in my recipes is as accurate as possible, but it might take you more or less time. You can use an oven thermometer to check that your oven is at the right temperature. I recommend tracking how your oven works and what tiny details you might need to adjust. Make ahead: Line the pan and freeze it for up to a month or refrigerate it for 3 or 4 days. Cover it well to prevent dryness.