Step 1

Preheat the oven to 375°F/190°C.

Step 2

Whisk together the flour, cream of tartar, baking soda, and salt in a large mixing bowl and set aside.

Step 3

Using a mixer, beat sugar and butter in a large bowl until light and fluffy. Scrape the sides of the bowl with a rubber scraper as needed.

Step 4

Add the eggs and beat until smooth and creamy, scraping the sides of the bowl with a rubber scraper as needed.

Step 5

Mix in the vanilla.

Step 6

With the mixer on low, gradually add the dry ingredients to the wet ingredients in three batches until just combined. The dough will be thick.

Step 7

Shape the dough into 1¼-inch balls. At this point, you can roll them in sugar or sprinkles or move on to the next step if you're making iced cookies.

Step 8

Place them 2 inches apart on an ungreased cookie sheet.

Step 9

For a flatter cookie – press the dough down slightly before baking with your palm or the bottom of a glass. For a puffier cookie, leave the balls intact.

Step 10

Bake for 8 to 10 minutes or until set. Remove from cookie sheet to wire rack to cool.

Step 11

Whisk together the ingredients for the icing, adding extra milk as needed, 1 teaspoon at a time, until desired consistency (a bit of milk goes a long way, so try to keep it slightly thick.)

Step 12

Spoon the icing on top of the cooled cookies.

Step 13

If using sprinkles, add them immediately to the wet icing. Let the icing harden before serving. You can store cookies for up to five days in an airtight container.