Preheat your oven to 350°F (175°C) and grease a tart pan.

In your food processor, combine the flour, powdered sugar, and salt; pulse until well combined.

Add cubed butter and sour cream, pulse until the dough clumps.

Press the dough into the tart pan and bake for 10 minutes until firm.

In a clean food processor, blend mascarpone, eggs, sugar, lemon zest, lemon juice, and sour cream until smooth.

Pour the filling into the baked crust and smooth it out.

Bake the tart for 30-35 minutes until set and lightly golden.

Cool the tart on a wire rack for an hour before serving.

Serve the tart at room temperature or chilled, optionally dusted with powdered sugar or served with berries.