Combine 1½ cups unbleached flour, ⅓ cup powdered sugar, and ¼ teaspoon salt in a food processor.
Cut ½ cup unsalted butterinto 8 slices and add to flour mixture, pulsing several times until the mixture resembles oatmeal. Add 1 egg yolk mixed with 1 tablespoon heavy cream.
Pulse until all ingredients are moistened. Then allow the machine to run a few seconds until the dough starts to stick together. (Add additional drops of cream if the dough seems too dry.)
Press dough into a roll like refrigerated cookie dough. Wrap in plastic and chill 30 minutes.
Spray molds generously with Baker's Secret or something like it. (Baker's Secret is an aerosol spray mix of flour and oil.) If using silicone molds, no greasing is necessary.
Slice the roll of dough into 12 pieces. Using a rolling pin, roll the dough between two pieces of plastic wrap into a circle slightly larger than tart molds. Press into a mold with fingers being careful to keep the thickness consistent. Use a knife to trim off any extra at the top. Freeze for at least 30 minutes, overnight or up to a month. (See video for this step.)
Place frozen tart shells on a cookie sheet. Press a small square of foil down into each crust and mold it to the shape of the crust. See the picture above.
Bake at 400˚F (200˚C)for 10 minutes. Remove foil and bake until golden brown, usually about 3-4 minutes.
Cream Filling:
Add 2¾ cups milk, ⅔ cup sugar, ¼ cup cornstarch, ⅛ teaspoon salt, and 4 egg yolks, to a blender or food processor bowl. (You can use a bowl and a whisk if that's all you have.)
Blend 5 seconds and pour into a 2-quart glass microwave-safe bowl.
Microwave 6-7 minutes on HIGH, whisking until smooth after 3 minutes, then every minute thereafter. (Keep microwaving if not thick after 7 minutes.)
Add 2 tablespoons unsalted butter and 1 teaspoon vanilla extract and whisk until smooth.
If not ready to assemble, cover the top of the warm custard with plastic wrap and smooth it to touch the surface. This prevents a skin from forming on top of the cream.
Assembly:
Fill each baked tart shells with cream filling. Top with fruit of your choice.
Glaze:
Melt ¼ cup currant jelly in a microwave or on top of the stove, and use a brush to dab some shininess on each piece of fruit. It's OK if some drips onto the cream.
Notes
NOTES:1. If dough in the food processor seems too dry to press into a ball, add a teaspoon or two of milk or cream.2. Tarts are best eaten the day they are assembled.3. A dollop of whip cream makes these even better.