Vanilla Frosted Brown Butter Cookie Bars

These cookie bars have all the deliciousness of a sugar cookie without the effort of cutting them out and frosting them perfectly.
Makes 12 large cookies

Method 

1. Preheat the oven to 325°F.
2. Place the butter in a medium saucepan over high heat and stir until melted. Cook for 3-4 minutes or until foamy and golden brown. Transfer to a bowl and set aside for 15-20 minutes to cool.
3. Place the browned butter and sugars in a medium bowl and, using an electric mixer, beat for 5 minutes or until well combined. Crack in the eggs one at a time, beating well after each addition.
4. Sift in the flour, baking soda, and cream of tartar. Beat on a low speed until just combined.
5. Roll the mixture between 2 sheets of non-stick baking paper to an 11 x 15 inch rectangle and place on a large baking tray.
6. Bake for 20-25 minutes or until golden brown and the center is still slightly soft. Allow to cool in the tray.
7. While the cookie cools, prepare the frosting. Cream the butter and powdered sugar together using an electric beater for 8-10 minutes or until light and fluffy. Add in the ground vanilla and beat for a further 3-4 minutes.
8. Once the cookie is completely cooled, spread the frosting over the cookie and slice into squares.