Cream together butter and sugars in a bowl with a hand mixer or with a stand mixer using the paddle attachment. Mix until light and fluffy. Then add egg and vanilla extract.
Whisk together dry ingredients in a small bowl and slowly add them to the creamed butter. Try not to overmix.
When dough comes together divide it into two flat discs and wrap in plastic wrap. Chill in the fridge for at least 60 minutes but overnight is best.
Preheat oven to 375 degrees F. Roll dough out until 1/4 inch thick. Cut out cookies and place on a baking sheet lined with parchment paper. I like to use a 3-inch cookie cutter for large sandwich cookies. You should get 12 large bottom layer cookies and 12 that you can cut a design in the middle. Bake cookies for 8-9 minutes until lightly browned around the edges.
Remove cookies and let cool completely before filling.
To make Strawberry Sandwich Cookies:
Optionally, sprinkle the top cookies with powdered sugar before making sandwich cookies.
Add 2-3 teaspoons of strawberry jam to the bottom layer of each sandwich cookie and top with the cut-out cookie.
Store cookies in an airtight container for 3-4 days.