Preheat oven to 325°. Line an 8-in. square baking pan with parchment, letting ends extend up sides; set aside. In a large bowl, beat the first 5 ingredients until blended. Stir in chocolate chips and walnuts. Spread into prepared pan., Bake until edges begin to brown and a toothpick inserted in center comes out with moist crumbs (do not overbake), 30-35 minutes. Cool completely in pan on a wire rack, at least 2 hours. Lifting with parchment, remove brownies from pan. Cut into bars. Store in an airtight container.