How to Make It
Combine raspberries, 1/4 cup granulated sugar, and 1 tablespoon water in a small saucepan. Bring to a boil. Reduce heat, and simmer 5 minutes or until berries break down and mixture thickens slightly, stirring frequently. Place cornstarch in a small bowl; add remaining 1 tablespoon water, stirring until smooth. Add cornstarch mixture to pan; cook 1 minute or until thick. Cool completely.
Preheat oven to 350°.
Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, baking soda, and salt in a bowl, stirring well with a whisk.
Place butter and remaining 1 cup granulated sugar in a bowl; beat with a mixer at medium speed until fluffy (about 5 minutes). Beat in vanilla. Add eggs, 1 at a time, beating well after each addition. Add flour mixture and buttermilk alternately to butter mixture, beginning and ending with flour mixture.
Spoon about 2 tablespoons batter into the bottom of each of 12 mini bundtlette cups coated with baking spray, spreading into an even layer. Drop about 3 tablespoons raspberry mixture evenly into each cup, spreading evenly on top of batter. Top evenly with remaining batter, smoothing tops with a spatula. Bake at 350° for 20 minutes or until a wooden pick inserted in centers comes out clean. Cool in pans on a wire rack 10 minutes; remove cakes from pans. Cool completely on wire rack.
Combine powdered sugar and 2 to 3 teaspoons water in a small bowl, stirring until smooth. Drizzle glaze evenly over cakes.
Bake a Second Batch
It's best to make one batch of cakes at a time (don't double the batter), though you can easily double the raspberry mixture.