Line a 9×13 inch (approx) pan with foil (or parchment if you prefer) and spray it with cooking spray or lightly grease it.

Gently melt the butter in a heavy 2-quart saucepan over low heat. Use a pastry brush to brush some of the melted butter up the sides of the pan — this helps prevent sugar crystals forming.

Add sugar, water, and corn syrup to the melted butter. Increase heat to medium‑high and bring the mixture to a boil, stirring until the sugar dissolves. Be gentle and try not to let sugar splash the sides of the pan (which can cause crystallisation).

Once the sugar is dissolved, clip on a candy thermometer. Cook over medium heat, stirring frequently, until the thermometer reaches 290 °F (soft‑crack stage) — this usually takes about 10‑14 minutes depending on your stove.

Immediately when it reaches 290 °F, remove from heat, stir in vanilla and salt quickly. Then pour the hot toffee into the prepared pan.

Evenly scatter the chocolate chips over the freshly poured hot toffee. Let them sit for ~2 minutes to soften, then use a knife or offset spatula to spread the melted chocolate into a smooth layer.

Top the melted chocolate with a generous sprinkle of finely chopped almonds. Let the pan sit at room temperature for about 3 hours (or until fully set).

Once set, lift the foil or parchment from the pan, remove it from the pan, take off the foil/parchment, and break the toffee into pieces. Keep the toffee in an airtight container to maintain freshness for up to two weeks.