Five-Spice Plum Cake

adapted from Cook’s Country
yield: one 6-inch cake

INGREDIENTS

3/4 cup blackberry jam, seedless
1/2 cup buttermilk, room temperature
1-1/2 tablespoons water
3/4 teaspoon five-spice powder
1/4 teaspoon ground cinnamon
1/4 teaspoon ground ginger
1-1/2 cups all-purpose flour
1/2 tablespoon baking powder
1/4 teaspoon fine sea salt
10 tablespoons (5 ounces) unsalted butter, softened
2/3 cups (about 4-5/8 ounces) granulate