These tarts are baked in black-pepper-flecked shortbread crusts and garnished with swirls of toasted meringue.
Make the crust: Preheat oven to 325 degrees. Coat six 4-inch and ten 3-inch round fluted tart pans with cooking spray. Place 4-inch pans on one rimmed baking sheet and 3-inch pans on another baking sheet.
With a mixer on medium-low speed, beat butter and sugar until just combined, about 30 seconds. Add flour, pepper, and salt, and beat 1 minute. Raise speed to medium-high, and beat until a dough forms, about 4 minutes.
On a lightly floured work surface, roll out dough to 1/4 inch thick. Cut out 31/4-inch circles and place in the 4-inch tart tins, pressing slightly to fill just the bottoms. Cut out 21/4-inch circles and place in 3-inch tart tins, pressing slightly to fill just the bottoms. Bake until pale golden brown, about 20 minutes. Let cool on sheets. (Leave oven on.)
Make the filling: Whisk egg yolks, lemon zest, lemon juice, condensed milk, and salt until smooth. Pour into tart pans. Bake until edges of filling are firm and slightly puffed, about 10 minutes for 3-inch tarts and 14 minutes for 4-inch tarts. Let cool. Refrigerate for 1 hour, then remove sides of tart pans (leaving the base), and refrigerate, uncovered, at least 4 hours, preferably overnight.
Preheat broiler. Remove bases from tarts, and return tarts to one baking sheet. Place meringue in a pastry bag fitted with a large star tip (such as Ateco #828). Pipe a dollop of meringue on top of each tart. Broil until top of meringue is just browned, about 30 seconds. (Alternatively, use a kitchen torch to brown meringue.) Serve immediately.
To cut out the dough rounds, you can use biscuit cutters or simply trace the bottom of the tart pan with a small knife.