Introduction

These Marshmallow Crispy Cookies are a delicious Costco copycat treat featuring a thin, buttery base loaded with mini marshmallows and crispy rice cereal. They combine chewy and crunchy textures with a delightful hint of browned butter and a sprinkle of flaky sea salt to balance the sweetness.

This image shows a close-up of four round oatmeal cookies on a white parchment-lined baking sheet with a dark, rustic metal edge. Each cookie has a golden-brown color with a rough, textured surface from the oats. The cookies have slightly uneven edges and visible white spots that look like melted marshmallow or white chocolate. Some coarse salt crystals are lightly sprinkled on top, adding a shiny effect. The baking sheet is placed on a white marbled surface. photo taken with an iphone --ar 4:5 --v 7

Ingredients

½ cup (113.5 g) salted butter
¾ cup (165 g) brown sugar
½ cup (100 g) granulated sugar
1 large egg, room temperature
1 teaspoon vanilla (vanilla paste is ideal if available)
½ teaspoon baking soda
¾ teaspoon salt
1 cup (158 g) + 2 tablespoons all-purpose flour
1½ cups (43 g) Rice Krispie cereal
⅔ cup (30 g) mini marshmallows
Flaked salt for topping

Instructions

Step 1: Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
Step 2: Brown the butter by melting ½ cup in a medium saucepan over medium heat. Continue cooking past the boiling point while stirring constantly until it turns golden brown with a nutty aroma. Watch carefully to avoid burning. Pour the browned butter into a bowl and chill in the fridge or freezer for about 10 minutes.
Step 3: In a medium mixing bowl, combine the cooled browned butter with brown sugar and granulated sugar. Add the egg and vanilla, then mix on low speed until smooth, about 30 seconds.
Step 4: Gradually add salt, baking soda, and flour to the mixture and stir gently to combine. Avoid overmixing to keep the cookies tender.
Step 5: Fold in the Rice Krispie cereal followed by the mini marshmallows carefully to avoid crushing them.
Step 6: Scoop dough into large balls using a 3-tablespoon cookie scoop, placing 4 to 5 cookies on each prepared baking sheet to allow space for spreading.
Step 7: Bake for 10 to 13 minutes until edges are lightly golden. Avoid overbaking to maintain a chewy center. Immediately sprinkle with flaked salt after removing from the oven.

Tips & Variations

For thicker cookies, add 2 extra tablespoons of flour to the dough.
Use vanilla paste instead of extract for a more intense vanilla flavor.
Measure flour by spooning it lightly into the cup rather than scooping to avoid packed flour and dense cookies.
Browning the butter adds a rich, nutty taste; don’t rush this step and watch closely to prevent burning.

Storage

Store the cookies in an airtight container at room temperature for up to 4 days for best freshness. To keep them longer, you can freeze the baked cookies in a sealed container for up to 2 months. Reheat briefly in the oven or microwave to bring back some softness and melty marshmallows.

How to Serve

The image shows a close-up view of nine oatmeal cookies arranged in three rows of three on a white tray lined with parchment paper. Each cookie is round with a golden-brown color, with a slightly uneven surface texture showing visible oats and small white patches of melted marshmallows embedded into the dough. Light sprinkles of coarse salt crystals are scattered on the tops, adding a subtle sparkle. The edges of the cookies are slightly darker and crispier, while the centers have a softer, chewier look. The tray rests on a white marbled surface. photo taken with an iphone --ar 4:5 --v 7

Serve this delicious recipe with your favorite sides.

FAQs

Can I use salted butter or unsalted butter?

Salted butter is recommended for this recipe to balance the sweetness and enhance flavor, but if you only have unsalted butter, add an extra pinch of salt when mixing the dough.

Will the mini marshmallows melt while baking?

The mini marshmallows soften during baking but generally hold their shape enough to add gooey pockets without completely melting into the cookie.