Preheat the oven to 350°F.
Line a large rimmed baking sheet with parchment paper.
Arrange the Ritz crackers in one flat layer.
Melt the butter in a saucepan over medium heat.
Add the brown sugar and cook for about 2 minutes, stirring until smooth and bubbling.
Pour the butter mixture evenly over the crackers.
Bake for 7–9 minutes, until the coating is bubbly.
Sprinkle the chocolate chips over the hot cracker layer.
Let the chocolate chips soften for 2–3 minutes.
Spread the softened chocolate into an even layer.
Scatter the mini marshmallows over the chocolate.
Sprinkle the graham cracker crumbs over the marshmallows.
Broil for 30–60 seconds, watching closely until the marshmallows are lightly golden.
Chill the bark for 20–30 minutes, until firm.
Break the chilled bark into pieces and serve.