Generously coat a bundt pan with melted butter, making sure to cover all the grooves well. Set aside.

In a medium saucepan over medium heat, add the butter and marshmallows. Stir constantly until completely melted and smooth.

Remove from heat and stir in the vanilla extract.

In a very large mixing bowl, add the popcorn, pretzel pieces, peanuts, and M&M’s. Gently toss to evenly distribute everything.

Pour the warm marshmallow mixture over the popcorn mixture. Using a spatula, carefully fold everything together until all the ingredients are coated.

Transfer the mixture into the prepared bundt pan. Place a piece of parchment paper over the top and press the mixture firmly into the pan to help it hold its shape and prevent sticking.

Cover the pan loosely with foil and allow the popcorn cake to cool and set for at least 1 hour. This helps the cake firm up, so it releases and slices cleanly.

When ready to serve, run a butter knife carefully around the edges of the pan to loosen the cake.

Turn the pan upside down onto a serving plate and lift the pan away. The cake should release easily.

Then the cake is ready to slice, serve and enjoy!