HEAT oven to 350° F. Combine flour, sugar, water, cocoa, 1/2 cup butter, eggs, baking powder, baking soda and vanilla in large mixer bowl. Beat at low speed, scraping bowl often, until moistened. Increase speed to high, scraping bowl often, until well mixed (1 to 2 minutes).
STIR in 1 cup chocolate chips by hand. Pour into greased and floured 13x9 inch baking pan. Bake for 30 to 40 minutes or until toothpick inserted in center comes out clean. Cool completely.
COMBINE 2/3 cup butter and peanut butter in medium bowl. Beat at high speed, scraping bowl often, until light and creamy (1 to 2 minutes). Reduce speed to low; add powdered sugar. Beat, gradually adding enough half-and-half for spreading consistency and scraping bowl often, until smooth (1 to 2 minutes).
FROST cooled cake; sprinkle with 1 cup chocolate chips and peanuts.