Special equipment: a 2-inch round cookie cutter
Put an oven rack in the center of the oven. Preheat the oven to 450 degrees F.
On a lightly floured work surface, roll the pizza dough into a 1/4-inch thick round. Using a 2-inch round cookie cutter, cut out 15 circles. Arrange the circles on a heavy baking sheet. Using the tines of a fork, prick the dough all over. Drizzle with olive oil and bake until golden brown, about 7 to 10 minutes. Remove from the oven and cool for 10 minutes.
In a small bowl, mix together the mascarpone cheese, sour cream and capers until smooth. Season with salt and pepper, to taste. Spoon about 1/2 teaspoon of the mascarpone mixture into the center of each pastry round. Top with a piece of smoked salmon and press gently.
Arrange the pizzettes on a platter and sprinkle with chopped chives just before serving.