Sugar Cookies: 

1. Preheat the oven to 350°F (177°C). Line a sheet tray with parchment paper or a silicone baking mat.
2. In a stand mixer fitted with a paddle attachment (or a large bowl with a hand mixer), cream together the softened butter and granulated sugar until fluffy, about 3-5 minutes. Add in the beaten eggs, vanilla extract, and milk and mix well to combine, scraping the bowl well after each addition.
3. In a separate large bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Add the dry ingredients to the wet ingredients and mix until just combined, scraping as needed.
4. Tightly wrap the cookie dough in plastic wrap, then refrigerate for at least 30 minutes before rolling it out.
5. After the dough has chilled, lightly flour your countertop and roll the cookie dough out to about a 1/2-inch thickness. Cut out the cookies using your desired cookie cutters, then transfer them to the prepared baking sheet.
6. Bake the cookies in the preheated oven for 8-12 minutes, or until they are lightly golden brown on the bottom. 
7. Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. Make sure the cookies are completely cool before decorating.

Vanilla Buttercream: 

1. In a stand mixer fitted with a paddle attachment (or a large bowl with a hand mixer), beat the softened butter until soft and fluffy, about 3-5 minutes. With the mixer still on, gradually add in the powdered sugar. Stop the mixer and scrape down the sides of the bowl with a spatula as needed to fully incorporate all of the sugar. 
2. Once the butter and sugar have been fully combined, add in the vanilla extract. Then, add in the milk 1 tablespoon at a time until you reach the desired consistency. If desired, add in food coloring in your desired color to color the buttercream. 
3. Spread the buttercream on top of the cooled cookies, then decorate with sprinkles if desired. Enjoy!