Step 1: Preheat Oven to 325. Mix the flaxseed with warm water and let it sit for about 5 minutes to thicken a little.
Step 2: Zest the lemon, you will need about a tablespoon for the icing. Squeeze the lemon and set the juice aside, you will need a tablespoon for the cake mix and a teaspoon for the icing.
Step 3: Mix butter, flax egg, a tablespoon of lemon juice, vanilla and rice milk until well incorporated. Fold in 1/2 cup blueberries. Bake at 325 for 22-25 minutes. Let fully cool before glazing.