Add the chocolate chips to a mixing bowl, along with the unsalted butter, half a tsp sea salt and half a tsp cinnamon. Pour over the sweetened condensed milk and stir to combine.
Pop the bowl in the microwave for a minute, so that it all melts together (you can also melt over a Bain-Marie or double boiler).
Gently stir the mixture together after (you don’t want air bubbles forming) until it is well combined. You want the texture to be richly-thick.
Grease a pan / baking dish or baking tin with butter and carefully line it with parchment paper or aluminium foil.
Pour the mixture into the pan slowly. Use a spatula to smoothen the surface. Sprinkle lots of sea salt on top.
Let the pan cool in the fridge for a few hours (or overnight).
Once completely set, the correct way to remove the fudge is by running a knife along the edge of the pan and lifting the fudge out holding onto the parchment paper. Once transferred onto a cutting board, carve our generous squares.