Line the base and sides of a 20 x 25cm slice pan with baking paper.
Place cream, vanilla beans and seeds into a medium saucepan over a medium heat and bring to the boil. Remove from the heat and cover to keep warm.
Place sugar, liquid glucose and water in a medium saucepan and heat to 145c. Test temperature using a candy thermometer. (If you do not have a thermometer, you can use a teaspoon to take a small amount of the glucose syrup and drop it into a bowl of chilled water. If the syrup is the correct temperature, it will separate and split into threads that will harden, but bend a little before breaking).
Once the syrup is the correct temperature, whisk in the butter and honey by hand.
Remove the vanilla beans from the cream mixture. Pour the warm cream mixture into the syrup in two or three stages, whisking continuously. This is to prevent the syrup mixture from dropping in temperature to lower than 110c.
Add the bicarb soda and continue to whisk until combined.
Place mixture over a medium heat and stir continuously for approx 20 mins until temperature reaches 119c. (If you do not have a thermometer, drop a little of the mixture into a bowl of chilled water. The mixture should be a firm but pliable texture).
Once the mixture is the right temperature, whisk in the dark chocolate vigorously until completely melted to ensure the sugar crystallizes and creates a fudgy texture when set. Gently fold through roasted hazelnuts.
Pour into prepared pan. Sprinkle lightly with Tasman Sea Salt Flakes.
Set aside at room temperature for 5 hours to set. Use a lightly oiled knife to cut fudge into squares.