Make the tartlet dough: In a bowl, whisk flour, powdered sugar, and salt.
Cut in the cold butter with a pastry cutter or your fingertips until sandy with pea-sized bits. Add the egg yolk and 1 tablespoon cold water. Mix just until it comes together, adding a second tablespoon of water only if dry.
Chill: Shape into a flat disk, wrap, and chill 30–45 minutes.
A cool dough prevents shrinking and keeps the crust tender.
Prep the pans: Lightly grease 8–10 mini tartlet tins (about 3–4 inches) or use a 12-cup muffin tin as a backup. Set on a baking sheet.
Roll and line: On a lightly floured surface, roll the dough to about 1/8 inch thick. Cut circles slightly larger than your tins.
Press into the tins, trimming excess. Prick the bases with a fork. Chill 10–15 minutes while you heat the oven to 350°F (175°C).
Blind bake: Line each shell with a small piece of parchment and fill with baking beans or rice.
Bake 10 minutes. Remove weights and bake 5–7 minutes more, until lightly golden. Cool slightly.
Make the pistachio cream: In a food processor, pulse pistachios and sugar until finely ground.
Add butter and blend until creamy. Add the egg, flour, salt, vanilla, and optional orange blossom water or zest. Process until smooth and spreadable.
Fill and bake: Spoon pistachio cream into the shells, about 2/3 full.
Smooth the tops. Bake at 350°F (175°C) for 12–15 minutes, until set and lightly puffed. Centers should not jiggle.
Cool completely in tins, then remove.
Add raspberries: Arrange raspberries on top of each tartlet, snugly packed for a neat look. Pointed ends up gives a classic finish.
Glaze for shine: Warm the apricot jam or jelly until fluid. If needed, thin with a teaspoon of water and strain.
Brush lightly over the berries to set and add gloss.
Garnish and serve: Sprinkle with chopped pistachios or a dusting of powdered sugar. Serve at room temperature when the flavors are most aromatic.