Put sugar, golden syrup and water in a small saucepan over medium high heat. Let the mixture boil without stirring. The sugar will dissolve and once it turns a medium amber, take off the heat.
Add the butter, stirring until melted, and then add the cream. Careful because it will sputter!
Finally, add the salt and vanilla. Let cool completely.
Chocolate Cupcakes
Preheat oven to 350°F/175°C. Put 12 cupcake cases in a 12-cupcake tray.
In the bowl of an electric mixer with the paddle attachment, cream the butter until smooth. Add the sugars and beat until fluffy and light, about 3 minutes. Add the eggs, beating well after each addition. Pour in the chocolate.
In a small bowl, whisk together the flour and baking soda. In a jug, mix the milk and vanilla together.
Add the dry ingredients and buttermilk/vanilla in three additions, beginning and ending with dry ingredients.
Fill the cupcake liners ¾ of the way, and bake for 20-25 minutes, a toothpick inserted should come out clean
Tahini Buttercream
In a mixer (or by hand!) using a paddle attachment, beat the butter and tahini until completely smooth.
Add the icing sugar, salt and vanilla. Beat for another 2-3 minutes until it is smooth.