Place spinach in a large microwave proof covered bowl. Microwave spinach on HIGH for 1 1/2 minutes on High. Cool until able to handle to squeeze out water (using hands). Puree in food processor with 1/2 cup water. (Makes about 1 cup pureed spinach)
In large bowl mix flour, cocoa powder, and baking powder. Set aside.
Melt butter and chocolate chips on low heat in medium sized pan.. Cool slightly. Add sugar and mix. Add 2 beaten eggs slowly to mixture and blend well without over stirring. Add spinach and vanilla.
Add wet mixture to flour mixture and stir until well blended.
Grease a 8-inch square pan. Spread mixture in pan. Bake at 350 degrees for 30 to 35 minutes until set. Cool before frosting.
FROSTING: In a large heatproof bowl, microwave the butter and cocoa powder until butter is melted. Beat together with a hand mixer until smooth. Add the vanilla and milk and stir. Add the confectioners sugar and stir, slowly at first, until incorporated; then beat on medium speed until frosting is smooth and creamy.
