Lofthouse Soft Sugar Sprinkles Cookies

INGREDIENTS:

1 large egg
1/2 cup unsalted butter (1 stick), softened
1/2 cup granulated sugar
1/2 cup light brown sugar, packed
2 teaspoons vanilla extract
1 3/4 cups cups cake flour, see directions (no substitutions, I used Swans Down)
2 teaspoons cornstach
1/4 teaspoon baking powder
1/4  teaspoon baking soda
pinch salt, optional and to taste
up to 1 1/2 cups sprinkles (reduce to 1 cup if you don't love sprinkles; I used 1 cup of larger jimmies and 1/2 cup minuscule nonpareils)

DIRECTIONS:

1. To the bowl of a stand mixer fitted with the paddle attachment (or large bowl and electric hand mixer), cream together the first 5 ingredients (through vanilla) on medium-high speed until light and fluffy, about 5 minutes.
2. Stop, scrape down the sides of the bowl, add 1 3/4 cups flour, cornstarch, baking powder, baking soda, optional salt, and mix on low speed until just incorporated, about 1 minute; don't overmix. Dough will be on the sticky and tacky side.
3. Mix in 1 cup sprinkles, and as desired, add remaining 1/2 cup.
4. Using a medium 2-inch cookie scoop, form heaping 2 to 3-tablespoon mounds (I made 15). Place mounds on a large plate, flatten slightly, cover with plasticwrap, and refrigerate for at least 3 hours, or up to 5 days, before baking. Do not bake with warm dough because cookies will spread and bake thinner and flatter.
5. Preheat oven to 350F, line a baking sheet with a Silpat or spray with cooking spray. Place mounds on baking sheet, spaced at least 2 inches apart (I bake 8 cookies per sheet) and bake for about 8 to 9 minutes, or until edges have set and tops are just beginning to set, even if slightly undercooked, pale and glossy in the center. Do not overbake because cookies will firm up as they cool. If cookies stayed domed while baking, tap gently a couple times with the back of a spoon to flatten. Allow cookies to cool on the baking sheet  for about 5 minutes before transferring to a wire rack to finish cooking. Cookies will keep airtight at room temperature for up to 5 days. Unbaked cookie dough can be stored airtight in the refrigerator for up to 5 days, or frozen for up to 4 months, so consider baking only as many cookies as desired and save the remaining dough to be baked in the future when desired.