Preheat your oven to 350°F. Line a baking sheet with parchment paper and set aside.
Prepare the Cookie Dough
Using a hand mixer, or stand mixer, cream butter and sugar together until light and fluffy. Add in vanilla and egg, and mix until well combined.
Take out two medium-sized size mixing bowls, and using a sifter, sift together flour, baking soda, baking powder, salt, and cornstarch, alternating between the two bowls until the flour mixture has been sifted 3 to 4 times. The flour should have a powder texture.
Gradually add the dry ingredients into the wet ingredients until blended. Scrape down the sides of the bowl as needed.
Cut Out and Bake the Cookies
Roll out the dough to ¼-inch thickness. Use a circular cookie cutter to cut out each cookie.
Place cookies on a prepared baking sheet and leave 2 inches between each cookie.
Bake for 7 to 9 minutes, until edges are lightly golden
Remove from the oven and set aside to cool.
Frost the Cookies
To make the frosting, beat the butter and powdered sugar until light and fluffy
Beat in the vanilla, milk, corn syrup, and food coloring until the frosting is smooth and spreadable.
Once cookies have cooled completely, spread frosting onto each cookie and then top with sprinkles.
Notes
Let the frosting set: Make sure the frosting has set before storing the cookies. Use baking soda and baking powder: This ensures your cookies will come out really soft and crumbly (what Lofthouse cookies are famous for!) Play with color: You can change the frosting color and/or sprinkles to make them your own.