Preheat your oven to 350°F and line a baking sheet with parchment paper.

Melt the butter and allow it to cool slightly.

In a large mixing bowl, whisk together the melted butter, brown sugar, and granulated sugar until smooth. Add the egg and mix until fully incorporated.

Add the flour, baking soda, and salt, stirring until a soft cookie dough forms.

Fold in ½ cup of Fruity Pebbles cereal, mixing just until evenly distributed.

Using a standard cookie scoop (about 2 tablespoons), scoop one portion of cookie dough onto your hand. Place one large marshmallow in the center, then top it with another scoop of cookie dough.

Pinch the edges of the dough together to completely seal the marshmallow inside, then gently roll the dough between your hands until smooth.

Pour the remaining ¼ cup Fruity Pebbles cereal into a shallow bowl and gently roll each cookie dough ball until lightly coated.

Place the cookies on the prepared baking sheet, leaving about 2 inches between each one.

Bake for about 13 minutes, or until the edges are lightly golden and the centers are just set.

Allow the cookies to cool on the baking sheet for 10 minutes before transferring them to a wire rack.

Serve warm for the ultimate gooey marshmallow center.