Adjust an oven rack to the bottom position. Preheat the oven to 400 degrees F.
Whisk the granulated sugar and cornstarch in a medium nonreactive saucepan. Add the lemon juice and 2 tablespoons of the bourbon; whisk until well blended. Stir in the cherries and cook over medium-high heat, stirring, until the mixture boils and thickens, and the cherries are nice and soft, about 12 minutes. Remove from the heat and let cool to room temperature, about 20 minutes.
Place one of the pie crusts on a parchment-lined baking sheet. Dock the center of the crust a few times with a fork. Add 1 cup of the cherry jam to the center of the crust and spread it evenly, leaving a 1-inch border. (Cover and refrigerate the remaining jam for up to 1 week.) Place the second pie crust on top, seal the edges, and dock the center three times with a fork. Bake until golden brown, 35 to 40 minutes. Let cool for 15 minutes.
While the tart is cooling, make the icing. Add the confectioners' sugar, half-and-half, vanilla and the remaining 2 teaspoons bourbon to a medium bowl. Whisk until thick and smooth. Using a rubber spatula, add the icing to the center of the cooling tart and spread it nearly to the edges. Sprinkle with the raw sugar and nonpareils, if using. Cut the tart into wedges and enjoy!