2 cups all-purpose flour
2 cups old-fashioned rolled oats
1 teaspoon baking soda
1 teaspoon cinnamon (Margaret uses apple pie spice)
1/2 teaspoon salt
1 cup unsalted butter (2 sticks) (Margaret uses margarine)
3/4 cup packed light-brown sugar
2 large eggs
1 teaspoon vanilla extract
Mix the batter: Heat the oven to 350°F. Whisk together the flour, rolled oats, baking soda, cinnamon, and salt in a medium-size bowl. Cream the butter and brown sugar in a large bowl with an electric mixer on medium speed. Beat in the eggs and vanilla. Gradually add the flour mixture to the butter mixture, beating on low speed just until well combined.
Bake the cookies: Drop the batter by tablespoonfuls onto a baking sheet, spacing about 2 inches apart. Bake the cookies just until lightly browned on the bottom and the tops are set—9 to 11 minutes. Don’t overcook, or they won’t be soft. Let the cookies sit on the baking sheet for 1 minute, then transfer them to a wire rack to cool. Store in an airtight container. Makes 30 three-inch cookies.