2 cups all purpose flour
1 teaspoon baking soda
3/4 teaspoon baking powder
1 teaspoon salt
1 cup (2 sticks) unsalted butter, softened to room temperature
1 cup granulated sugar
1 cup packed light brown sugar
2 teaspoons vanilla extract
2 3/4 cups rolled oats
1 1/4 cup chocolate chips or chunks
3/4 cup chopped walnuts
Preheat the oven to 350° Fahrenheit. Line two baking sheets with parchment paper, or grease them well.
Measure the flour, baking soda, baking powder, and salt into a bowl and whisk to combine. Set aside.
Using a stand mixer with the paddle attachment, or a wooden spoon, beat the butter, granulated sugar, and brown sugar for a few minutes, until lighter in color and fluffy. Scrape the bottom and sides of the bowl as needed. Add the eggs and vanilla, and stir to combine. Gradually add the reserved dry ingredients, then add the oats, chocolate and walnuts, and stir until just combined.
Shape the cookies into ping-pong-sized balls, and place on the cookie sheets with some space between. Smoosh with the heel of your hand to form 1/2-inch thick disks.
Bake for 10 minutes, rotating the pans halfway through the baking time. Cook until the edges of the cookies are golden brown, but the centers appear blond and slightly underdone. Let the cookies cool slightly on the baking sheets, then transfer to racks. Enjoy right away, or pack to bring with you as gifts on your cross-country flight.