Line an 8x8-inch (for thicker fudge) or 9x9-inch (for slightly thinner fudge) square baking pan with parchment paper or foil, leaving overhang on two sides to create handles. Lightly coat the lining with nonstick cooking spray so the fudge releases easily.

Using a lightly oiled knife or kitchen scissors, cut the gumdrops or spice drops into small, pea-sized pieces. Place them in a bowl and toss with 1–2 tablespoons powdered sugar until they are lightly coated and no longer sticking together. Set aside.

In a medium, heavy-bottomed saucepan over low heat, combine the white chocolate chips, sweetened condensed milk, and unsalted butter. Stir gently and constantly with a rubber spatula or wooden spoon, scraping the bottom and corners of the pan to prevent scorching.

Continue cooking over low heat, stirring constantly, just until the mixture is completely melted, smooth, and glossy with no visible lumps of white chocolate. If it begins to thicken or look like it may overheat, remove the pan from the burner and let the residual heat finish melting the chocolate.

Remove the saucepan from the heat. Stir in the vanilla extract and fine sea salt until fully incorporated. Taste a tiny bit carefully (it will be hot) and adjust the salt slightly if you prefer a more balanced sweet-salty flavor.

Let the fudge mixture sit off the heat for about 3–4 minutes, stirring occasionally. It should remain warm and pourable but not so hot that it melts or dulls the color of the gumdrops when they are added.

Gently fold the powdered sugar–coated gumdrop pieces into the warm fudge mixture. Use a light hand so the candies stay suspended throughout the fudge instead of sinking to the bottom. If the mixture seems very thin, let it stand another minute or two to thicken slightly before transferring to the pan.

Pour the fudge mixture into the prepared pan, spreading it evenly into the corners with an offset spatula or the back of a spoon. If desired, press a few extra gumdrop pieces gently into the top so they are visible after cutting.

Refrigerate the fudge for at least 2–3 hours, or until firm to the touch in the center. For the cleanest slices and best texture, chill it overnight.

Use the parchment or foil overhang to lift the chilled fudge out of the pan and onto a cutting board. With a sharp chef’s knife, cut into approximately 1-inch squares, wiping the knife clean between cuts. Serve chilled or at cool room temperature.