Place Brie cheese in the freezer for 20 minutes. Oil a mini muffin pan with cooking spray.

Roll 1 puff pastry sheet out into a 10x14-inch rectangle. Cut the sheet lengthwise into 4 even strips and crosswise into 6 even strips; there should be 24 squares. Separate and press them gently into the muffin cups.

Cut chilled Brie cheese into 24 pieces approximately 3/4-inch in size. Add 1 teaspoon cranberry sauce to each pastry-lined muffin cup; press in 1 piece of Brie and top with 1 teaspoon of chopped walnuts. Sprinkle bites with sea salt. Chill for at least 30 minutes and up to 3 days.

Preheat oven to 400 degrees F (200 degrees C).

Bake bites in the preheated oven until golden brown, 18 to 20 minutes.