Prep your tools. Line two baking sheets with parchment paper. Preheat your oven to 350°F (175°C). Set the butter out ahead of time so it’s soft but not greasy.

Cream the butter and sugars. In a large bowl, beat the softened butter, granulated sugar, and brown sugar until fluffy, about 2 minutes. This helps create that soft, bakery-style texture.

Add eggs and vanilla. Beat in the eggs one at a time, then add vanilla. Scrape down the bowl so everything mixes evenly.

Mix dry ingredients. In a separate bowl, whisk flour, cornstarch, baking soda, and salt. Cornstarch keeps the cookies thick and tender.

Combine wet and dry. Add the dry mixture to the wet ingredients and mix on low until just combined. Don’t overmix—stop as soon as the flour disappears.

Add the color. Add blue gel food coloring, starting with 1 teaspoon. Mix until evenly tinted. Add more if you want a deeper blue. Gel gives color without watering down the dough.

Fold in the fun. Stir in chocolate chips, white chocolate chips (if using), chopped mini cookies, sandwich cookie pieces, and M&M’s or sprinkles. Fold gently so the cookies don’t turn to dust.

Scoop the dough. Use a large cookie scoop (about 3 tablespoons) for big bakery-style cookies. Place on prepared sheets, leaving space—these spread a little.

Top for looks. Press a few extra chips and mini cookie pieces on top of each dough ball. This makes them look loaded and picture-ready after baking.

Chill briefly (optional but helpful). If your kitchen is warm, chill the scooped dough for 15–20 minutes to keep the cookies thick.

Bake. Bake for 10–12 minutes, until edges are set and centers look slightly underdone. They’ll finish cooking on the sheet.

Finish and cool. Let cookies rest on the sheet for 5–7 minutes, then move to a rack. The centers will set into a soft, chewy texture.