Begin by gathering all your ingredients and ensuring your workspace is tidy. Line a 9x9 inch baking dish with parchment paper, allowing some overhang to easily lift the toffee later. Preheat your cooking area.

Spread a generous layer of chopped pecans or almonds evenly on the bottom of your prepared dish.

In a heavy-bottomed pot, combine the butter, granulated sugar, water, and salt. Heat over medium to medium-high heat, stirring continuously until the mixture is melted, bubbly, and begins to caramelize, about 5–7 minutes.

Attach a candy thermometer to the pot without touching the bottom. Continue cooking until it reaches the hard crack stage at 300°F, approximately 10–15 minutes.

Once your toffee mixture reaches temperature, swiftly remove it from the heat. Carefully stir in the vanilla extract.

Working quickly, pour the hot toffee mixture over the layer of nuts in your prepared dish and spread it evenly.

Sprinkle chocolate chips over the hot toffee surface, immediately cover the dish to trap the heat, and let it sit for about 5 minutes.

Once the chocolate is melted, uncover the dish and gently swirl the chocolate across the toffee using a spatula. Optionally sprinkle extra chopped pecans and flaked sea salt on top.

Allow your Classic Christmas Toffee to cool completely at room temperature for about 4 hours. Once cooled, lift the parchment out of the dish and cut into squares.