Zucchini Brownies Recipe

In a large bowl, cream butter and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in yogurt and vanilla. Combine the flour, cocoa, baking soda and salt; gradually add to creamed mixture. Stir in zucchini. Pour into a greased 13-in. x 9-in. baking pan. Bake at 350 ° for 35-40 minutes or until a toothpick inserted near the center comes out clean. For frosting, in a small saucepan, combine chocolate chips and peanut butter. Cook and stir over low heat until smooth. Spread over warm brownies. Cool on a wire rack. Cut into bars.