Preheat the oven to 425 degrees F. In a bowl, stir the raspberries, 2/3 cup sugar, the vanilla seeds and lemon juice. Let sit for 15 minutes. Strain (save the liquid for a cocktail mixer).
Using a 3-inch cutter, cut 18 circles from the pie dough. Dollop 2 tsp. berry mixture on each. Brush the edges with beaten egg and fold in, pressing to seal.
Using a spatula, transfer the tarts to a parchment-lined baking sheet; dollop with the butter. Brush the dough edges with more egg; sprinkle with sugar. Bake until bubbling, about 15 minutes.