Preheat oven to 350°F. Prepare a cookie pan with parchment paper. Arrange blueberries in a single layer. Cut a large slit in a second sheet of parchment paper and cover blueberries to prevent splattering. Cook for 15 minutes or until fragrant. Cool completely. Transfer fruit and juices to food processor and blend until smooth. If blueberry puree is less than 1-1/4 cups, add enough water to reach 1-1/4 cups. Refrigerate until cold.
Decrease oven temperature to 325°F. Prepare 3 - 6 in. round pans with parchment paper. Do not spray the pans.
For cake, whip egg whites with electric mixer on high speed until foamy. Add cream of tartar and 1/3 cup sugar, 1 tablespoon at a time, and continue whipping until glossy and whites hold stiff peaks.
In large bowl, sift together flour, remaining 1/3 cup sugar, baking powder and salt.
In small bowl, whisk together milk, egg yolks and violet and vanilla extracts. Stir into flour mixture until just combined. Fold 1/3 of beaten egg whites into yolk mixture to loosen, then fold in remaining egg whites until no streaks remain. Divide evenly into prepared pans.
Bake 23-27 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes on cooling rack; remove from pan and cool completely.
For icing, beat Whipped Icing Mix, 2 tablespoons water, and cold blueberry puree for 4-6 minutes on high speed, or until well combined and fluffy.
To assemble cake, cut each cake layer in half horizontally. Fill and ice cake layers with roasted blueberry icing.