PREHEAT oven to 375F. Line a rimmed baking sheet (11 × 17 in.) with parchment. Arrange 1 layer of pretzels, breaking into pieces to fit.
COMBINE butter, sugar, corn syrup, vanilla and salt in a medium saucepan over medium. Cook, stirring occasionally with wooden spoon, until mixture starts to boil. Stop stirring and boil for 5 min, brushing sides of pot with a pastry brush dipped in cold water. Quickly pour caramel back and forth over pretzels, spreading to cover. (It doesn’t need to fully cover.)
BAKE until caramel spreads and starts to bubble around the corners, about 12 min. Remove baking sheet from oven (if some pretzels float to the top, quickly rearrange). Immediately cover with chocolate chips. Let stand for 3 min. Spread melting chocolate over the toffee (hardened caramel). Sprinkle with nuts and dried fruit, then drizzle with white chocolate. Cool for 30 min. Refrigerate until chocolate is firm, about 30 min. Break into large shards. Toffee will keep well, frozen in resealable freezer bags, up to 2 weeks.