Start by measuring out 1 cup of mushroom popcorn and popping it according to package instructions. Place it in a large mixing bowl to cool slightly.

In a large saucepan, combine 1/2 cup of salted butter, 1 cup of light corn syrup, and 1 cup of light brown sugar over medium heat. Stir until mixture starts to boil.

Allow to boil for about 5 minutes, then whisk in 1 cup of sweetened condensed milk and optional food coloring. Monitor until it reaches 240°F on a candy thermometer.

Remove from heat and quickly pour caramel over the popped popcorn. Gently mix with a wooden spoon to coat.

Coat your hands with butter and take small portions of the coated popcorn to shape into balls about 3 to 4 inches in diameter.

Place formed popcorn balls on a parchment-lined baking sheet and allow to cool completely for about 30 minutes.