1. In a bowl, with an electric mixer on medium speed, beat butter, granulated sugar, and brown sugar until smooth. Add vanilla and eggs and beat until well blended.
2. Stir in flour, salt, and baking soda until well combined. Stir in butterscotch chips, chocolate chips, and walnuts. Spread batter evenly in a buttered 9- by 13-inch baking pan.
3. Bake in a 350° oven until a wooden skewer inserted in center comes out with moist crumbs attached, about 30 minutes. Let cool on a rack for 15 minutes, then cut into 24 bars.
Note: Nutritional analysis is per bar.