Ingredients
Equipment
Method
Make the cookie bars
- Preheat the oven to 350°F.
- Line a 9x13-inch baking pan with parchment paper, leaving overhang on two sides, and lightly coat the parchment with nonstick cooking spray.
- Whisk the flour, baking powder, and salt together in a medium bowl.
- Beat the softened butter and granulated sugar in a large bowl with a mixer on medium speed until light and fluffy, about 2 minutes.
- Beat in the egg and 2 teaspoons vanilla until combined.
- Mix in the flour mixture on low speed just until no dry streaks remain.
- Press the dough evenly into the prepared pan.
- Bake for 20 to 24 minutes, until the edges are lightly golden and the center looks set.
- Cool completely in the pan on a wire rack, about 1 1/2 hours.
Make the frosting
- Beat the 1/2 cup butter in a bowl with a mixer on medium speed until creamy, about 1 minute.
- Add the powdered sugar, milk, and 1 teaspoon vanilla, and beat on low until combined, then on medium until fluffy and pipeable, about 2 minutes.
- Beat in green gel food coloring a little at a time until the frosting is a deep green.
Decorate the bars
- Lift the cooled cookie slab from the pan and cut it into 12 bars, making 3 columns and 4 rows.
- Spoon the frosting into a zip-top bag, snip off a 1/2-inch corner, and pipe a zigzag tree shape onto each bar, widening the zigzags toward the bottom.
- Place one yellow star-shaped sprinkle at the top and one mini chocolate chip at the bottom of each frosted tree.
Notes
Let the cookie slab cool completely before frosting so the trees hold their shape. Store covered in the refrigerator for up to 5 days; freeze the unfrosted bars or finished bars for up to 2 months. For a dairy-free variation, use dairy-free butter and milk.
