In a large bowl, cream together the softened butter, brown sugar, and white sugar on medium-high speed until light and fluffy (about 2 minutes).

Add the egg and vanilla extract, and beat until completely smooth and combined.

In a separate bowl, whisk together the flour, cornstarch, baking soda, and salt. Gradually add to the wet ingredients, mixing on low until just combined.

Gently fold in the chocolate chips and Easter sprinkles with a spatula.

Take about 2 tablespoons of dough, flatten it into a disc, and place one marshmallow Peep in the center. Fold the dough around the Peep, pinching the seams tightly so the marshmallow is completely enclosed. Roll into a smooth ball.

Place the stuffed dough balls on a parchment-lined tray, cover loosely, and chill in the refrigerator for at least 1 hour.

Preheat oven to 350°F (175°C). Place chilled dough balls 2-3 inches apart on a parchment-lined baking sheet.

Bake for 11-13 minutes until the edges are golden brown but the centers are still soft. Do not overbake, or the marshmallow will melt into the dough.

Let cool on the baking sheet for 10 minutes before transferring to a wire rack. Serve warm for a gooey marshmallow pull!