Cover a baking sheet with parchment paper or a silicone baking mat.
Add butter, sugar, and salt to a medium saucepan set over medium-low heat. Cook while stirring intermittently until butter is completely melted, sugar is dissolved, and mixture has turned a brown peanut butter-like color, 10-15 minutes. If you're using a candy thermometer, mixture should register between 290-300 degrees. Remove from heat and stir in vanilla.
Pour mixture over baking sheet, spreading into a rectangle.
Sprinkle chocolate chips over the toffee mixture. Let sit for about 2 minutes before using an offset spatula to spread into an even layer. While you're waiting to spread chocolate, melt white chocolate chips in the microwave.
Drizzle melted white chocolate over the toffee and use a knife to swirl it around. Top with candy corn and sprinkles. Let toffee cool for at least 2 hours before breaking into pieces.
Store in an airtight container at room temperature.