Add lemon juice to taste, plus sugar, a pinch of salt, and one grind of black pepper. Refrigerate. Shortbread: Place the butter and confectioner’s sugar in a standing mixer and beat until creamy.

Stir until the sugar has dissolved, then add the sumac and black pepper. Simmer gently for 5 minutes, then remove from the heat. Cool, then strain through a fine sieve. If the strawberries are ...