Preheat oven to 350 degrees F. For crust: In a medium bowl, combine crushed graham crackers, the 1/4 cup sugar, and the finely chopped peanuts. Stir in the 1/2 cup melted butter. Press mixture evenly into the bottom of an ungreased 11X7X1-1/2-inch baking pan. Bake for 5 minutes; cool.

For filling: In a heavy large saucepan, combine the 1/2 cup butter and the chocolate; heat and stir over low heat until melted. Remove from heat. Add the 1 cup sugar, the eggs, and vanilla to chocolate mixture; stir just until combined. Stir in flour and peanut-butter-flavored pieces. Spread evenly over crust.

Bake for 20 minutes. Cool in pan on a wire rack. Spread with Peanut Butter Frosting. Cut into bars. Place a peanut half on each bar.

Peanut Butter Frosting: In a medium bowl, combine 1/4 cup butter and 2 tablespoons peanut butter; beat with an electric mixer on low speed for 30 seconds. Gradually add 1 cup powdered sugar, beating well. Beat in 1 tablespoon milk and 1/2 teaspoon vanilla. Gradually beat in 1 cup powdered sugar and enough milk to make a frosting that spreads easily.

Makes: 20 brownies

To Bake Ahead: Bake as directed; do not cut bars. Cover and chill for up to 2 days.

Test Kitchen Tip: Let these peanut-butter-and-chocolate bars cool completely before cutting. If you cut them while they are still warm, moisture will escape as steam and the brownies may be dry.