Easy and fun! Took this to a church party and it was an instant hit!

Preheat your oven to 350°F (175°C) and grease a 12-cup muffin pan.
In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.
Beat in the egg and vanilla extract until well combined.
In another bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the chocolate chips. If using nuts, fold them in as well.
Divide the cookie dough evenly among the muffin cups, pressing the dough down slightly to form cups.
Bake for 10-12 minutes, or until the edges are just set and the centers are still slightly soft.
Remove the muffin pan from the oven and immediately press a few mini marshmallows into the center of each cookie cup. The residual heat will melt the marshmallows slightly, creating the 'rocky road' effect.
Let the cookie cups cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.
Variations & Tips
Feel free to customize these Rocky Road Cookie Cups to your liking! You can use dark chocolate chips or white chocolate chips for a different flavor profile. If you're not a fan of nuts, simply leave them out or replace them with dried fruit like cranberries or raisins. For an extra indulgent touch, drizzle some melted chocolate over the top of the cooled cookie cups.