Preheat The Oven & Prep Your Pans. Start by preheating the oven to 350 degrees F. Line a 9x13 inch metal pan with parchment paper, with parchment hanging over the two long sides to use as handles later. (You can use metal binder clips to hold the parchment "handles" out of the way)

Combine The Dry Ingredients. In a medium bowl, combine gluten-free flour blend, cornstarch, and salt. Whisk to combine and set aside.

Cream The Butter, Cream Cheese & Sugar. In the bowl of a stand mixer (or in a large bowl with a hand mixer), combine softened butter, cream cheese, and sugar. Cream together 2-3 minutes or until light, fluffy, and smooth.

Add Egg, Vanilla & Almond Extract. Mix in the room temperature egg, vanilla and almond extract.

Mix In Dry Ingredients A Little At A Time. Turn the mixer on low and add the flour about 1/3 of a time, until all of the dry ingredients have just been mixed into the wet ingredients.

Spread Out The Dough. Transfer the cookie dough to the prepared baking pan. The dough will be very thick and sticky, so you'll want to work slowly. Mist an offset spatula with spray oil (or get your fingertips the slightest bit wet and shake off any excess water. Gently spread the dough out into an even layer and smooth it as level as you can. The dough will be very sticky and thick, but taking your time to do this well means your bars will be GORGEOUS. (An offset spatula makes this easier!)

Bake & Cool Completely. Pop the pan in the oven and bake for 20-24 minutes, or until the edges are set and the middle looks just done. Try not to over-bake, since the cookies will continue to bake after you remove them from the oven. Cool the bars completely before making the frosting. (Otherwise the frosting will melt) 

Cream Butter & Cream Cheese. In a stand mixer or large bowl with a hand mixer, combine butter and cream cheese. Beat for 2-3 minutes, or until smooth and light.

Add Powdered Sugar & Cream. Then, add 2 1/2 cups powdered sugar and 1 Tablespoon cream. Mix for 30 seconds or so on medium-low speed to incorporate, then add another 2-2 1/2 cups of powdered sugar and mix until just incorporated.

Mix In Vanilla, Almond Extract, & Salt. Pour in the vanilla extract and vanilla extract and add the pinch of salt. Increase the speed to medium-high and beat for 1 full minute. Add up to 1 more tablespoon cream, if needed.

Add Color, If Using. If you like, add a tiny bit of food coloring to the frosting and mix in until smooth and blended. For the light pink I did in these photos, dip a toothpick into red gel food coloring and wipe most of it off onto a plate, paper towel, or piece of parchment paper. Then, wipe the remaining food coloring on the toothpick into the frosting and mix it in, adding more red color from the plate as needed until you reach your desired color. 

Frost & Decorate The Cookie Bars. Pipe or spread the frosting onto the cooled sugar cookie bars and top with sprinkles, if desired. Store the frosted cookie bars covered in the refrigerator 2-3 days, or freeze up to 1 month.