Chocolate Half Birthday Cake with Naturally Purple Frosting

Today was Cora's half birthday and to celebrate we had the usual half birthday cake. When I asked her what kind of cake she wanted a few days ago she said "Chocolate Cake with Purple Icing." I immediately thought, "How can I make purple icing without food coloring?" Well, it didn't take too much searching to figure it out and now I have a technique I can use for every occasion. I LOVED the color of this cake and Cora did too. And even better, it tasted FANTASTIC! This will be my new go-to chocolate cake recipe and I'll be playing with icing colors for years to come :)

Chocolate Cake
from Betty Crocker's Cookbook, Bridal Edition

2 1/4 C flour
1 2/3 C sugar
3/4 C butter, softened
2/3 C baking cocoa
1 1/4 C water
1 1/4 t baking soda
1 t salt
1 t vanilla
1/4 t baking powder
2 large eggs

Heat oven to 350. Grease bottom and sides of rectangular pan, 13x9x2 inches, 2 round pans, 9x1.5 inches, or 3 round pans, 8x1.5 inches, with shortening. Lightly flour (I used baking cocoa instead of flour).
Beat all ingredients with electric mixture on low speed for 30 seconds, scraping bowl constantly. Beat on high speed for 3 minutes, scraping bowl occasionally. Pour into pan(s).
Bake rectangle 40 to 45 minutes, rounds 30 to 35 minutes, or until toothpick inserted in center comes out clean. Cool rectangle in pan on wire rack. Cool rounds 10 minutes; remove from pans to wire rack. Cool completely, about 1 hour.
*To make the half birthday cake I baked two 9-inch round cakes, cut each in half from the top to make four halves, and stacked them with frosting between the layers.

Naturally Purple Buttercream Frosting

Begin by placing about 1 1/2 to 2 cups of frozen blueberries in a pan on the stove. Cook over low heat until blueberries burst and release their juices. Smash and strain thru a sieve to obtain blueberry juice. (you can add the blueberry pulp to some yogurt for a snack if you'd like!) Cool completely.
Next, make a double batch of Vanilla Buttercream Frosting, adding only 2 tablespoons of milk. Replace the remainder of the milk with your reserved blueberry juice until you reach the desired color of frosting. If your frosting gets too thin add more powdered sugar. Then frost and enjoy! The blueberries give the frosting a gorgeous purple color and a only a very slight hint of fruity flavor.