Using cake flour is important to this recipe, but if you have cornstarch you can mix a little with some all-purpose flour to substitute for cake flour.
1 cup plain nonfat yogurt
1/4 cup fresh sqeezed lemon juice (grate zest first)
1 1/3 cups organic cane sugar
5 tablespoons plus 1 tsp (1/3 cup) butter
1 tablespoon grated lemon zest
1 1/2 teaspoons baking powder
1/2 teaspoon baking soda
1/4 teaspoon salt
2 large eggs plus white of 1 large egg, room temperature
2 1/4 cups cake flour
Preheat oven to 350 degrees F. Coat a 12-cup bundt pan with nonstick spray. Mix yogurt and lemon juice in a small bowl until blended. Set aside.
In a large bowl, beat sugar, butter, lemon zest, baking powder, baking soda and salt with mixer on medium speed to blend (mixture will resemble damp sand). Beat in eggs and egg white until smooth. On low speed, beat in yogurt, then flour, until just blended. Scrape into pan; smooth top.
Bake 30 minutes, or until a wooden pick inserted in cake comes out clean. Cool in pan on wire rack 15 minutes before inverting on rack. Serve warm or cool. Good served with strawberries.