In the work-bowl of a food processor, pulse the butter, salt, sugar, and flour until the mixture reaches a crumb-like texture, about 15 to 20 seconds. Add the sour cream and process until the dough comes together, about 10 seconds.
Remove dough from food processor and pat the dough together into a ball. Wrap dough with plastic wrap and chill in the fridge for 10 to 15 minutes.
Preheat oven to 375° F. On a floured surface, roll out the dough until it is no thicker than 1/4-inch. Use a round cookie cutter (or get creative and use the tart pan like I did) and cut circles about 4-inches in diameter.
Place the dough rounds into ungreased tartlet pans, and push down gently with your fingers so the dough is centered in the well and the dough comes up the sides about 1/2-inch. Prick the bottom of the dough with a fork twice. Fill each tart with two tablespoons of Bleuberet Strawberry Rhubarb “Bharbie” Jam. Spread evenly.
Re-roll remaining pastry dough and use a cookie cutter to make heart-shaped pastry cutouts. Place in the center of each jam-filled tart.
Place tart tins on top of a cookie sheet and bake for 18 to 20 minutes, or until the tart shells begin to turn golden.
Let tarts cool completely. Before serving the tarts, dust with confectioners’ sugar. Tarts will keep in an airtight container for up to 3 days after baking.
Don't have tart tins? These jam tarts can also be made in a muffin tin! Cut pastry dough into circles about 3-inches in diameter and decrease baking time to 15 minutes.