Melt Butter and Marshmallows: Place a large pot over low heat and add the butter. Melt completely, then add in the mini vegan marshmallows and stir until smooth.

Combine Rice Krispies: Remove the pot from heat and fold in the Rice Krispies cereal, mixing gently to coat each piece with the marshmallow mixture.

Fold in Blueberries: Add the fresh blueberries to the pot and gently fold them into the mixture without breaking them apart.

Press Mixture into Pan: Prepare a greased 9x9-inch baking pan and press the Rice Krispies mixture firmly to create an even layer.

Prepare Vanilla Glaze: In a mixing bowl, whisk powdered sugar, milk, and vanilla extract until smooth and pourable.

Drizzle Glaze: Once the mixture has cooled for 10-15 minutes, drizzle the vanilla glaze over the top and spread evenly.

Set and Cut Bars: Allow the bars to cool completely for 30 minutes, then cut into squares and serve or store in an airtight container.