- 1 cup (2 sticks) unsalted butter, room temperature
- 1 1/4 cups granulated sugar
- 2/3 cup packed light-brown sugar
- 1 large egg
- 1/2 teaspoon pure vanilla extract
- 1 1/2 cups all-purpose flour
- 1 1/4 teaspoons coarse salt
- 1/2 teaspoon baking powder
- 1/4 teaspoon baking soda
- 3 cups Cornflake Crunch
- 2/3 cup mini chocolate chips
- 1 1/4 cups mini marshmallows
Cream together butter and both sugars in the bowl of an electric mixer fitted with the paddle attachment on medium-high, 2 to 3 minutes. Scrape down sides of bowl and add egg and vanilla; beat for 7 to 8 minutes.
With the mixer on low, add cornflake crunch and chocolate chips; mix until just combined, 30 to 45 seconds. Add mini marshmallows and mix until just incorporated.
Line a baking sheet with parchment paper. Using a 2 3/4-ounce ice-cream scoop or 1/3-cup measuring cup, portion dough out onto prepared baking sheet. Pat tops of cookie domes flat. Wrap baking sheet tightly with plastic wrap and refrigerate for at least 1 hour and up to 1 week. Do not bake cookies from room temperature or they will not hold their shape.
Preheat oven to 375 degrees. Line additional baking sheets with parchment paper or non-stick baking mats.
Arrange chilled dough at least 4 inches apart on prepared baking sheets. Transfer to oven and bake until puffed, cracked, spread, and browned on the edges, about 18 minutes. Let cool completely on baking sheets.