Crush the graham crackers into fine crumbs using a food processor or place them in a ziplock bag and crush with a rolling pin.

In a medium saucepan, melt the butter over low heat. Once melted, add the crushed graham crackers and stir until well combined.

Press the graham cracker mixture into the bottom of a 9x13 inch dish to form a crust layer.

In the same saucepan, mix the rhubarb, sugar, cornstarch, and water. Cook over medium heat, stirring often, until the mixture thickens and the rhubarb softens.

Once the rhubarb mixture is ready, pour it over the crust and spread it evenly.

In a separate bowl, whip the heavy cream until soft peaks form. Fold in the mini marshmallows and vanilla pudding gently.

Spread the creamy mixture over the rhubarb layer, smoothing it out evenly.

Refrigerate the bars for at least 4 hours or until set.

Once the bars are set, cut them into squares and serve chilled. They pair beautifully with fresh fruit or a drizzle of caramel sauce.