Preheat oven to 375°.
Grease a 9 x 13 inch baking dish.
Melt 1 cup of the chocolate morsels in a microwave-safe bowl for 1 minute. Continue this process with 10 second intervals until the chocolate is just melted. Stir between each interval. Set to the side and let cool to room temperature.
Mix together flour and baking powder in a separate small bowl.
Beat sugar, vanilla, and softened butter together in a large mixing bowl until combined. It will be crumbly.
Beat in the two large eggs.
Add in the melted chocolate and mix until smooth.
Gradually mix in the flour and baking soda mixture.
Pour the batter into the greased baking dish.
Bake for 10-12 minutes or until mostly set. The inside will still be a little gooey.
Remove from the oven and top with the mini-marshmallows and remaining 1 cup of chocolate morsels. Return to the oven for 2-3 minutes. Just until the marshmallow start melting.
Cool for 15-25 minutes. Cut into bars and serve!