Directions

1. Preheat oven to 350F (175C).
2. In a bowl, whisk flour, oats, baking powder, baking soda, and salt.
3. In a separate bowl, cream butter and sugars until fluffy.
4. Beat in egg and vanilla extract.
5. Gradually add dry ingredients to wet and mix until combined.
6. Drop tablespoons of dough onto baking sheets and flatten slightly.
7. Bake for 12 to 15 minutes until edges are golden.
8. Cool completely before assembling filling.
9. For filling, beat butter until creamy, add powdered sugar, milk, and vanilla until smooth.
10. Spread filling on bottom of one cookie and top with another to make sandwich.