3/4 cup blueberry preserves, plus 1 tablespoon melted preserves
Confectioners' sugar, for dusting
Preheat the oven to 350°. Butter and flour a 10-inch Bundt pan. In a medium bowl, whisk together the flour, baking powder and salt. In a large bowl, beat the butter until creamy. Add the granulated sugar and beat until fluffy. Beat in the eggs, sour cream and vanilla. Beat in the dry ingredients just until incorporated.
Spread all but 1/2 cup of the batter into the prepared pan. Using the back of a spoon, make a trough in the batter, all the way around the pan. Mix the 3/4 cup of blueberry preserves with the reserved batter and spoon it into the trough.
Bake the cake for about 1 hour, or until it begins to pull away from the pan and a skewer inserted in the center comes out clean. Let the cake cool in the pan for 15 minutes. Invert the cake onto a wire rack, remove the pan and let cool completely. Sift the confectioners' sugar over the cake, drizzle with the melted blueberry preserves and serve.