Colorado Cowboy Cookies

2 cups all purpose flour
2 cups old-fashioned oats
1 teaspoon baking soda
1/2 teaspoon baking powder
1/2 teaspoon salt
1 cup (2 sticks) unsalted butter, room temperature
3/4 cup sugar
3/4 cup plus 2 tablespoons packed dark brown sugar
2 large eggs
1 teaspoon vanilla extract
1 1/2 cups semisweet chocolate chips
1 cup chopped toasted walnuts (about 4 ounces)

Whisk first 5 ingredients in medium bowl to blend, then set aside. Using an electric mixer, beat the butter and both sugars in a large bowl until light and fluffy. Add eggs and vanilla. Mix thoroughly. Add dry ingredients and beat until just blended. Stir in chocolate chips and walnuts. Cover dough and chill 1 hour. Preheat oven to 350°F. Form dough into balls, using 1/4 cup dough for each. Place on greased baking sheets, spacing 2 inches apart. Flatten with hand to 3 1/2-inch rounds. Bake 10-15 minutes or until cookies are golden brown around edges and firm in center. Transfer to cooling racks to cool completely