Butterscotch Pudding Parfait with Gingersnap Crumble

Name: Butterscotch Pudding Parfait with Gingersnap Crumble
Ingredients: 2 cups whole milk, divided; 1 cup packed dark brown sugar; 1 1/4 teaspoons kosher salt; 4 large egg yolks; 1/4 cup cornstarch (about 1 1/8 ounces); 2 tablespoons (1 ounce) dark rum or Scotch whiskey; 2 teaspoons vanilla extract; 1/2 cup cold unsalted butter (4 ounces), cut into 1/2-inch pieces; 1 cup heavy cream; 1/2 cup crème fraîche or sour cream; 3 tablespoons powdered sugar; 1/4 teaspoon vanilla extract; 2 cups gingersnaps (about 6 3/4 ounces), crushed (about 1 3/4 cups)