Old-Fashioned Christmas Toffee

Prep the pan and toppings. Line a rimmed baking sheet (a half-sheet pan is perfect) with parchment or a silicone mat. Set it near the stove. Have chocolate chips and nuts ready, because once the toffee is done, it moves fast. Safety note: hot sugar burns, so keep kids and pets out of the zone.

Start the toffee base. In a heavy saucepan over medium heat, combine butter, sugar, water, corn syrup (if using), and salt. Stir until the butter is melted and the sugar looks fully moistened.

Cook to hard-crack. Attach a candy thermometer if you have one. Cook until the mixture reaches 300°F and turns a rich amber, about 10 to 15 minutes. Stir frequently to prevent scorching, especially as it darkens, and try not to scrape the sides of the pan (that can invite graininess). If it starts to darken too quickly, lower the heat slightly.

Flavor and pour. Turn off the heat. Carefully stir in vanilla (it may bubble). Immediately pour the toffee onto the prepared baking sheet. Tilt the pan to spread; if it starts setting before it evens out, use an offset spatula to gently nudge it into a thin, even layer. Expect a fairly thin slab on a half-sheet pan.

Add chocolate. Sprinkle chocolate chips evenly over the hot toffee. Let them sit 2 to 3 minutes until glossy and melty, then spread into an even layer with an offset spatula or butter knife.

Top and set. Sprinkle nuts over the chocolate and gently press them in. Let toffee cool at room temperature until fully set, about 1 hour. For faster setting, refrigerate 15 to 20 minutes, but avoid long chilling. Condensation can make chocolate look streaky.

Break and enjoy. Lift the slab out by the parchment and break into pieces. For cleaner shapes, you can score the warm chocolate lightly with a knife once it starts to set, then snap along the lines later. Store airtight with parchment between layers.