Cream the butter and sugar together in the bowl of an electric mixer on low speed. (Use the paddle attachment). Mix until thoroughly incorporated - for about one minute. Scrape down the sides of the bowl with a plastic spatula and mix again for a few seconds more. Over mixing the butter and sugar in this step will cause too much air to be incorporated into the dough. If you'd like a light and fluffy cookie, that's ideal, however the dough will spread more during baking; not ideal if you'd like the cookie to hold its shape.
Add eggs slowly and mix. Scrape down the bowl with your spatula at least once and mix again. Add vanilla extract. Stir briefly.
Add all of the flour to the bowl. Place a large tea towel between the edge of the bowl and the electric mixer so that the flour won't escape. Mix on low speed for 30 seconds. Remove the tea towels and observe the dough mixing; when it starts to come together add the rainbow baking chips and mix until the dough clumps around the paddle attachment. The dough should peel away from the sides of the mixer and clump around the paddle attachment. You can also test the dough by pinching it between your thumb and index finger. If it’s soft but not sticky, it’s just right. If it’s too sticky when you pinch it between your fingers, add flour, ¼ cup at a time, and mix until you’re happy with the texture.
Roll the dough out between 2 large pieces of parchment paper. Place on a baking sheet and into the fridge or freezer for a minimum of 1 hour.
Cut out cookie shapes. Place on parchment paper-lined baking sheets. Re-roll scraps and repeat. If your dough gets too soft to work with, place in the fridge or freezer periodically to firm up again.
Once all cut out, put cookie dough shapes back into the fridge or freezer for 10 minutes to 1 hour to chill again. They will then hold their shape better when baked.
Preheat your oven to 350°F or 176°C.
Bake cookies for 8-12 minutes or until the edges become golden brown. The baking time will depend on the size of your cookie.
Let cookies cool to room temperature and decorate if you like! If you’re new to decorating cookies, here is a cookie decorating tutorial with everything you’ll need to know to begin!