Step 1

Scoop ice cream into a large bowl; stir ice cream until slightly softened, about 2 minutes. Stir in fudge, pretzels, toffee candy bar, and lemon peel until evenly combined. Cover and freeze until firm, at least 3 hours or up to 12 hours.

Step 2

Stir together sugar and 1/4 cup water in a medium saucepan. Cook over medium, stirring constantly, just until sugar dissolves, about 1 minute and 30 seconds. Continue to cook, without stirring, until sugar mixture turns amber in color, 7 to 10 minutes. Gently swirl pan once, and carefully whisk in butter cubes. Remove from heat; gradually whisk in cream, vanilla, and salt. Let cool about 15 minutes.

Step 3

To serve, scoop ice cream evenly into 4 bowls. Drizzle each with about 2 tablespoons caramel sauce; reserve remaining sauce for another use. Garnish sundaes with additional fudge, pretzels, toffee candy bar, and lemon peel.