Cover a baking or casserole dish (approx. 20 x 20 cm) with lightly buttered baking paper. In a heavy-bottomed saucepan, melt condensed milk, butter, sugar, maple syrup and salt over medium heat. Raise the temperature and cook the mixture to a thick caramel consistency. Stir constantly with a wooden spoon so that nothing sticks to the bottom of the pan and burns. The mixture must reach a temperature of at least 115 degrees.
As soon as the caramel has reached this temperature (this can take 30 – 40 minutes) you can remove the pot from the burner after 1-2 minutes. Now stir in the Taunus-Tropfen and the chocolate and continue to stir vigorously until the mixture has combined and is smooth again. Pour the mixture into the prepared mold and sprinkle with a few pinches of sea salt flakes. Allow to cool at room temperature.
When done, the fudge should be firm to the touch. Store in a screw-top jar or cookie jar in a cool place.