Toffee

Prep the pan. Line a 9×9-inch baking pan with parchment paper, leaving a slight overhang on two sides to make the toffee easier to lift out later.

Melt the base. In a heavy-bottomed medium saucepan, combine the butter, sugar, water, and salt. Place over low heat, stirring gently and frequently with a wooden spoon or heatproof spatula until the butter is completely melted and the mixture is smooth.

Prevent crystallization. Before the mixture boils, dip a pastry brush in warm water and brush down any sugar crystals clinging to the sides of the pan. (This helps keep the toffee from seizing or turning grainy.)

Bring to a boil. Increase the heat to medium. Continue stirring gently as the mixture comes to a steady boil. Be patient — don’t crank up the heat, which can cause scorching.

Cook to hard crack. Clip a candy thermometer to the side of the pan, making sure the tip does not touch the bottom. Cook, stirring occasionally, until the mixture thickens, turns a deep golden color, and reaches 305°F (151°C, hard crack stage). This can take 10–15 minutes.

Add vanilla & pour. Immediately remove the pan from the heat and carefully stir in the vanilla extract (the mixture will bubble vigorously). Quickly pour the hot toffee into the prepared pan, tilting or spreading it with a spatula into an even layer.

Top with chocolate. Let the toffee sit for 5 minutes, then sprinkle evenly with the chocolate chips. Cover the pan loosely with foil or an inverted baking sheet for another 5 minutes to trap heat. Remove cover and use a spatula or offset knife to spread the melted chocolate into a smooth, even layer.

Finish & cool. Sprinkle with chopped almonds and flaky sea salt, if desired. Let the toffee cool completely at room temperature until the chocolate is firm (you can refrigerate briefly to speed this up, but room temp gives the best snap). Once set, lift the toffee from the pan using the parchment overhang, break into pieces, and serve.