Preheat oven to 350°F. Spray 9-inch spring form pan with cooking spray.
In saucepan, bring blueberries, sugar and cornstarch to a boil over medium-high heat. Reduce heat to medium-low and simmer until thickened, about 10 minutes, stirring occasionally. Remove from heat and let cool.
Cake Instructions
Beat butter and sugar until light and fluffy. Add eggs, one at a time, beating after each addition. Stir in flour, baking powder, baking soda and salt until blended. Beat in sour cream and vanilla until smooth. Stir in lemon zest. Transfer batter to prepared spring form pan and bake 30 minutes.
Remove cake from oven and carefully spread blueberry mixture over top of cake.
Crumb Instructions
In bowl combine flour, sugar, brown sugar and cinnamon. Stir in melted butter. Using hands, shape into crumbs and arrange over blueberry mixture.
Return cake to oven and bake 45 minutes or until toothpick inserted in center comes out clean. Cool 30 minutes in pan. Run knife around edges of pan and release from sides. Transfer to wire rack and cool completely. Sprinkle with confectioners’ sugar, if desired.