Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

Melt 1 stick of unsalted butter in a medium saucepan over low heat. Stir occasionally until melted, then add 1 cup of brown sugar and cook for 3-5 minutes until bubbly and smooth.

Remove from heat and stir in 1 teaspoon of vanilla extract and a pinch of salt until combined. Set aside to cool slightly.

In a large mixing bowl, pour in 6 cups of Chex cereal and drizzle the warm toffee mixture over it. Fold gently to coat the cereal evenly.

Spread the mixture on the prepared baking sheet and bake for about 15 minutes, stirring halfway through.

Let cool completely on the baking sheet before transferring to a serving bowl or airtight container.