Alternate adding flour mixture and tomato purée to the batter, starting and ending with the flour. Be sure to incorporate fully before doing the next addition.
Pour batter into prepared pan and bake for 40 minutes, or until a toothpick comes out clean.
Let cake cool in pan 10 minutes, then invert onto a rack and cool completely.
To make the glaze, mix together powdered sugar, vanilla, and 2-3 tablespoons leftover tomato juice until completely smooth. Add more sugar or liquid as necessary. Drizzle over cooled cake.
1 1/2 cup powdered sugar, 1/2 teaspoon pure vanilla extract