Heat oven to 350°F. Spray 13×9-inch pan with cooking spray; line with cooking parchment paper, leaving a few inches of overhang on each side. In a large bowl, beat eggs with electric mixer on medium-high speed 1 minute. Slowly beat in granulated sugar, then beat 4 minutes longer. Eggs should be pale in color and fall in thick ribbons back into bowl.

In another bowl, mix flour, baking powder and salt. Add to egg mixture all at once; beat on low speed just until incorporated. In small bowl, beat together 1 cup milk, the melted butter and 1 teaspoon vanilla. Add to mixture in 2 additions.

Pour batter in pan.

Bake 35 to 40 minutes or until cake is golden and center springs back when lightly pressed. Cool in pan 15 minutes, then use overhanging parchment to carefully lift cake out of pan, and transfer to rack to cool completely, about 1 hour. Meanwhile, beat powdered sugar, softened butter, 3 tablespoons milk and 1 teaspoon vanilla to make smooth frosting.

Spread chopped peanuts on small pan or plate.

Use serrated knife to cut cake into 24 squares (6 rows by 4 rows). Frost top and sides of each square with frosting, then roll in chopped peanuts, using hands if necessary to press peanuts into frosting.

Refrigerate 30 minutes to firm up. Serve cold, or remove from refrigerator 20 minutes before serving.