Ingredients:

  • 1 (15.25 ounce/432g) box yellow cake mix
  • ½ cup (1 stick/113g) unsalted butter, melted
  • 1 large egg
  • 1 cup (2 sticks/226g) unsalted butter
  • 1 cup (200g) granulated sugar
  • 2 tablespoons milk
  • 1 teaspoon vanilla extract
  • ½ cup (85g) chopped pecans or walnuts (optional)
  • ½ cup (85g) semi-sweet chocolate chips

Instructions:

  1. Preheat oven to 350°F (175°C). Grease and flour, or line with parchment paper, a 9x13 inch baking pan.
  2. In a large bowl, combine the cake mix, melted butter, and egg. Mix until just combined; don't overmix.
  3. Press the cake mix mixture evenly into the prepared baking pan.
  4. Bake for 15 minutes, or until lightly golden.
  5. While the base is baking, melt the butter, sugar, and milk in a saucepan over medium heat, stirring constantly.
  6. Bring the mixture to a boil, stirring constantly. Continue to boil for 3 minutes, stirring constantly to prevent burning. Remove from heat and stir in the vanilla extract.
  7. Remove the partially baked base from the oven. Pour the toffee mixture evenly over the base.
  8. Sprinkle with chopped pecans or walnuts, if using.
  9. Return to the oven and bake for another 10-15 minutes, or until the toffee is bubbly and golden brown. Watch carefully, as it can burn easily.
  10. Remove from oven and immediately sprinkle with chocolate chips. Let stand for a few minutes until the chocolate softens, then spread evenly.
  11. Let the bars cool completely in the pan before cutting into squares. Chilling in the fridge can help for cleaner cuts.