The recipe i have found doesn't have toffee chips but i have given it a shot anyway
1/2 cup (110 grams) popcorn kernels or about 10 cups of popped corn
1 1/2 cups (300 grams) granulated white sugar
1/2 cup (110 grams) packed dark brown sugar
1/2 cup (120 ml) light corn syrup
1/2 cup (120 ml) water
2 tablespoons (28 grams) butter
2 teaspoons kosher salt
2 teaspoons baking soda
Caramel Corn: Preheat the oven to 120 degrees F (49 degrees C) and place the oven rack in the center of the oven. Pop the corn and place in a large stainless steel bowl that has been lightly buttered or sprayed with a non stick cooking spray. Place the bowl, with the popcorn, in the oven (this will keep the popcorn warm).
In a large heavy bottomed saucepan, stir together the sugars, corn syrup, and water. Place the saucepan over medium heat and bring to a boil, stirring occasionally. Once the mixture boils, cover, and boil the mixture for about one to two minutes. (This allows steam to form which then condenses and washes off any sugar crystals that have attached themselves to the sides of the saucepan.) Uncover the saucepan and clamp a candy thermometer to the side of the saucepan. Boil the mixture over medium heat, stirring occasionally, until the temperature reaches the soft ball stage, 240 degrees F (116 degrees C). At this point, stir in the butter. Continue to cook the caramel, stirring occasionally, until the temperature reaches the hard crack stage, 300 degrees F (149 degrees C). (Brush down the sides of the pan, with a heatproof pastry brush that has been dipped in warm water, to remove any sugar crystals that may have formed on the sides of the saucepan
Then remove the saucepan from the heat and carefully stir in the salt and baking soda. (The caramel will foam up when you add the baking soda so be very careful.) Pour the caramel over the popcorn and toss, with two heatproof spatulas or wooden spoons (not your fingers), to evenly coat the popcorn. The caramel corn will be in large clumps so spread the caramel corn onto a large sheet of aluminum foil. Then, while the caramel corn is still hot, separate it into bite-size pieces, with two forks or by wearing heatproof gloves. Cool completely and then store in an airtight container, at room temperature, for about 10 days.
Makes about 8 servings