Line a 9x13-inch baking pan with parchment paper.

In a medium saucepan, melt butter over medium heat. Add sugar, salt, and water. Stir constantly until mixture comes to a boil.

Using a candy thermometer, cook to 300°F (hard crack stage), stirring occasionally.

Remove from heat and stir in vanilla extract.

Pour toffee into prepared pan, spreading evenly with a spatula. Let cool for 5–10 minutes.

Sprinkle chocolate chips over warm toffee. Let sit 1–2 minutes, then spread melted chocolate evenly.

Sprinkle toasted almonds over chocolate layer and press lightly. Add sea salt if desired.

Cool completely at room temperature or refrigerate. Break into pieces and store in airtight container.