Preheat your oven to 350°F.
In a medium oven-safe skillet or baking dish, melt the butter over medium heat.
Once melted, remove from heat and add the chocolate chips, spreading them evenly across the bottom.
Top the chocolate chips with the mini marshmallows, covering them completely.
Arrange the sliced strawberries and blueberries on top of the marshmallows for a festive look.
Bake in the preheated oven for 10-12 minutes, or until the marshmallows are golden brown and the chocolate is melted.
Remove from the oven and let cool for a few minutes before serving.
Serve warm with graham crackers for dipping.