Step 1

Preheat the oven to 350°F.

Step 2

Prepare a 9 x 13-inch baking pan by lining with parchment paper.Leave some paper hanging over the sides, to hold when removing the bars from the pan. Set aside.

Step 3

To the bowl of a stand mixer fitted with a paddle attachment (or a large mixing bowl and electric hand mixer), add butter and sugar. Set the mixer to medium-high power and mix until creamy and well combined. Add whole egg, egg yolk, and both extracts, and mix again to combine.

Step 4

With the mixer running on low power, slowly incorporate flour, baking powder, baking soda, and salt.

Step 5

Once a cohesive dough forms, mix in 1 tablespoon red jimmies and 1 tablespoon green jimmies. Reserve the rest for garnishing.

Step 6

Press dough into the prepared baking dish.Bake for 23-25 minutes, or until edges begin to look golden brown.

Step 7

Remove from the oven and let the cookie bars cool completely in the baking dish, so they finish baking and the center sets up. Meanwhile, prepare the frosting, following the directions shown below.

Step 8

Add softened butter to a medium mixing bowl. Using a mixing spatula or electric hand mixer, beat well to get rid of any lumps.

Step 9

To the bowl, add vanilla and salt, and beat again to combine.

Step 10

Slowly incorporate powdered sugar, mixing very well to thoroughly combine and remove any lumps.

Step 11

Once bars are cool, use your hands to hold two sides of parchment paper and lift the cookie out of the baking dish. Transfer to a large cutting board.

Step 12

Using an offset spatula, spread an even layer of frosting over the cookie. Garnish with remaining red and green jimmies.

Step 13

If desired, use a sharp knife to cut off the edges, then cut the remaining cookie into 12 squares.