Marbled Valentines Day Cookies

Place room-temperature butter, (salt if unsalted butter) and 1 cup of granulated sugar in stand mixer with paddle attachment and mix on low until smooth. Creamed butter should be fluffy and pale yellow in color.
Add 1 large egg at room temperature and mix on medium (4 on Kitchenaid mixer) in stand mixer until fully incorporated. Scrape bowl when necessary to make sure egg incorporates.
Add 1 tsp of vanilla extract. Mix until just incorporated.
In a separate bowl, whisk dry ingredients (AP flour, baking powder, nutmeg) together.
Add dry ingredients into stand mixer with a scoop (about 1/3 of total dry ingredients at a time) and mix until fully incorporated. Start mixer on slow until flour starts to incorporate, then turn up to medium. Scrape bowl as needed to fully incorporate.
Add 1 tsp of milk once flour is fully incorporated. Continue to mix on slow until dough becomes a solid mass.
Scrape out mixer bowl, wrap up sugar cookie dough in plastic wrap and chill in refrigerator for 2 hours.
Knead cookie dough and roll out cookie dough until thin to cut cookie shapes. Use a cookie cutter to cut out uniform shapes.
Place cookies on a baking sheet lined with parchment paper. Put cookie sheet back in refrigerator for about 15 minutes to chill again.
Bake chilled cookies at 350ºF for 10-14 minutes depending on size of cookie. Cookies will be slightly golden brown on the edge. Chilled cookie dough will keep it's shape in the oven and not expand or warp.

Combine your egg whites, sifted powdered sugar, and cream of tartar in the bowl of your stand mixer with the whisk attached.
Mix on low to get the ingredients combined then bump up to high for 1-2 minutes. Add in your vanilla extract and whip until it's white. No need to mix for longer than 5 minutes.
Place the royal icing into a bowl or container with a lid. Your THICK royal icing is now ready to be thinned down to the consistency you desire.
Add water 1 tsp at a time until a ribbon of royal icing goes flat in 15 seconds.
Color 1/3 of your royal icing hot pink or whatever color you desire.
Drizzle your hot pink icing over the top of the white icing and dip your cooled sugar cookies onto the surface. Pull straight up and tap off any excess icing. Wipe the edges clean.
Let cookies dry completely before packaging. They do not need to be refrigerated.

Ingredients