Preheat your oven to 350°F (175°C). Grab a large baking sheet and line it with parchment paper. Set these aside for now.

In a large mixing bowl, add the softened butter, eggs, milk, and vanilla extract. Mix these wet ingredients together until they are well combined and smooth.

Pour the entire box of cake mix into the bowl with the wet ingredients. Gently combine the cake mix into the wet ingredients until just combined. Be careful not to overmix.

Gently fold in the blueberries into the cookie dough using a spatula. If you’re using frozen blueberries, there’s no need to thaw them first. Just fold them in while they are still frozen. Be gentle to avoid smashing the blueberries too much.

Using a cookie scoop or a spoon, drop rounded tablespoons of cookie dough onto your prepared baking sheet. Leave a little space between each cookie, about 2 inches, so they have room to spread out while baking. If desired, roll each dough ball in powdered sugar before placing it on the baking sheet.

Place the baking sheet in the preheated oven and bake for 10-12 minutes, until the edges are lightly golden brown and the centers are set.

Once baked, remove the baking sheet from the oven and let the cookies cool on the baking sheet for about 5-10 minutes. Carefully transfer the Blueberry Cake Mix Cookies to a wire rack to cool completely.