Step 5: The Last Ingredient...
Upon removing the toffee mixture from the microwave for the final time, you should smell a delicious buttery aroma, the scent of the nuts, and a lovely golden-brown colour.
Add in your teaspoon of baking soda and mix it in with the spatula. You'll immediately notice a change in colour and an increase in volume.
The baking soda needs to be fresh, otherwise you risk the defluffing of your toffee, and it will become super dense and practically inedible.