Preheat oven to 350 degrees F. Spray a tube pan with nonstick spray.
In a small saucepan, combine the blueberries, 1/3 cup sugar and cornstarch. Cook over medium heat 5 to 6 minutes, or until thick- stirring constantly. Remove from heat and set aside.
In a large bowl, use an electric mixer to combine the butter and sugar. Add the eggs one at a time, beating well after each.
In a separate bowl, whisk together the flour, salt and baking powder. Add to the butter mixture beating it in alternately with the sour cream. Stir in the extract.
Spoon half of the mixture into the prepared pan. Spoon half of the blueberry mixture into the pan. Add the remaining batter, then blueberries. Swirl with a knife gently. Sprinkle with pecans, if using.
Bake 50 minutes. Let stand 5 minutes before removing from pan. Place on a serving dish.
Prepare glaze: Whisk glaze ingredients in a small bowl. Drizzle over top of the cake.
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