Prepare the pan: Line a baking sheet (about 16x10 inches or 9x13 inches) with parchment paper.
Melt the base: Combine the salted butter and white sugar in a non-stick saucepan over medium heat. Stir continuously. Keep stirring even if the mixture looks grainy until it turns clear and reaches a golden amber color (or about 290°F–305°F on a candy thermometer).
Add flavor and lift: Remove the pan immediately from the heat. Carefully stir in the vanilla extract and baking soda. The mixture will bubble up.
Pour and set: Pour the hot toffee onto your prepared parchment-lined pan and spread it thin.
Add chocolate and nuts: Let it cool slightly, then add chocolate (either by laying chocolate over the hot surface to melt and spreading it out, or dipping cooled broken pieces into tempered chocolate) and finish with chopped almonds.
Cool and break: Let it set completely until hard, then break it into pieces.