Preheat oven to 350F and line baking sheets with parchment paper or silicone baking mats. Set aside.
In a large bowl, beat butter and sugar together until well-combined
Add egg, egg yolk, and vanilla extract. Beat until well-combined.
Add flour, cream of tartar, baking soda, and salt.
Stir in just until combined.
Add food coloring, and stir in just until combined.
Scoop dough into tablespoon-sized scoops.
Roll in granulated sugar and then in powdered sugar.
Place 2" apart on prepared baking sheets.
Bake for 8-10 minutes. The edges should be set, and the centers should be soft.
Immediately gently press a heart sprinkle into each cookie.
Remove to wire racks to cool.
Notes
Butter - I use salted butter. If using unsalted butter, add an additional 1/4 teaspoon of salt.
Egg yolk - The egg yolk helps to add a bit of chew to the cookies.
Vanilla extract - Feel free to add more vanilla if you'd like.
All-purpose flour - It's important to properly weigh the flour. Either weigh it or sift/stir it to break it up. Then lightly spoon into a measuring cup and level.
Green food coloring - Green gel food coloring or regular green food dye will work.
Granulated sugar - The granulated sugar helps add flavor.
Heart sprinkles - I used candy red heart sprinkles with a small heart inside of a bigger heart (affiliate link). I liked the heart within a heart since the Grinch's small heart grows three sizes in the movie.