In a heavy bottom or stainless steel sauce pan melt the sugar, butter, salt, and vanilla over medium-low heat. Be sure to stir this mixture constantly.
Cook and stir constantly until hard-crack stage of 295-300F, measured using an instant read or candy thermometer.
Carefully remove the pot from the heat and stir in the baking soda. STIR VIGOROUSLY. The baking soda will puff up as it adds tiny bubbles into the toffee.
Once it puffs up, immediately pour the mixture onto the baking sheet.
DO NOT TOUCH THE TOFFEE. It will burn you. But you can use a spatula or offset spatula to level the top.
Melt the chocolate with coconut oil over a bain marie. Pour on top of the toffee and spread it evenly using the spatula or offset spatula.
Sprinkle with the cinnamon sugar while the chocolate is still hot.
Let stand 2 hours at room temperature until cooled completely or chill for 30 minutes.
Break into bite-size pieces using your hands and serve chilled or at room temperature.
Toffee can be stored in an airtight container at room temperature or in the refrigerator for two weeks. If you find the toffee melting, it means your house is very warm and you should refrigerate it. It also keeps well in the freezer for a month.