In a large bowl, with mixer at medium speed, beat first 8 ingredients until blended, occasionally scraping bowl with rubber spatula. Reduce speed to low; add flour and beat just until blended. Preheat oven to 350 degrees. Drop dough by heaping tablespoon, about 2 inches apart, on 2 ungreased large cookie sheets. Top cookie dough with chopped peanut brittle pieces, gently pressing peanut brittle halfway into dough. Place cookie sheets on 2 oven racks. Bake cookies 15 to 20 minutes until lightly browned, rotating cookie sheets halfway through baking time. Cool 2 minutes on cookie sheets on wire racks; with pancake turner, remove cookies to wire racks to cool completely. Store cookies in tightly covered container.