To Make Cookies:
Preheat oven to 350°F. Line a cookie sheet with parchment paper; set aside. Remove bags of white chocolate and gumdrops from jar; set aside. Empty the remaining contents of the jar into a large bowl. Stir in 1 egg, 1/2 cup softened butter, and 1 teaspoon vanilla until combined. Shape dough into 40 about 1-inch balls. Place balls 2 inches apart on the prepared cookie sheet. Using your thumb, make an indentation in the center of each ball. Place a gumdrop in each indentation. Bake about 10 minutes or until edges are firm. Cool on cookie sheet for 1 minute. Transfer cookies to a wire rack; cool. In a small saucepan cook and stir white chocolate over low heat until melted. Spoon white chocolate over tops of cookies to cover gumdrops. Let stand until chocolate is set.
To Make Ahead:
Store jar of mix in a cool, dry place for up to 1 month.
Layer cookies between sheets of waxed paper in an airtight container; cover. Store at room temperature for up to 3 days or freeze for up to 3 months.