Crust
37 gingersnap cookies, coarsely broken (about 9 ounces; about 3 1/4 cups plus 2 tablespoons of pieces)
6 tablespoons unsalted butter, melted

Filling
1 8-ounce container mascarpone cheese
6 ounces cream cheese, room temperature
1/4 cup sour cream
1/4 cup sugar
1 teaspoon grated lemon peel
1/4 teaspoon vanilla extract
1 tablespoon finely chopped crystallized ginger (optional)

Topping
4 to 5 small nectarines, halved, pitted, cut into thin slices
1/4 cup peach jam, warmed
2 tablespoons finely chopped crystallized ginger (optional)