Frosted Sugar Cookie Bars

Ingredients

• 1 cup (2 sticks) unsalted butter, softened
• 2 cups white granulated sugar
• 2 tablespoons milk
• 1 teaspoon vanilla extract
• 3 large eggs
• 4 cups all-purpose flour
• 3 teaspoons baking powder
• 1 teaspoon kosher salt
• 1/2 cup (1 stick) unsalted butter, softened
• 8 ounces cream cheese, softened
• 1/4 teaspoon kosher salt
• 1 teaspoon pure vanilla
• 4-5 cups powdered sugar
• 1–2 tablespoons milk
• Rainbow sprinkles