When the color turns golden brown, immediately remove from heat and pour in the boiling water. (Note: This takes 10-15 minutes)
Return to the heat and stir until the caramelized sugar dissolves in the water.
Remove from heat, stir in fluer de sel, and cool completely.
In a small mixing bowl, sift together flour, baking soda and salt. Set aside.
In a separate mixing bowl, mix cooled caramel syrup, egg, sugar, melted butter and milk. Stir well until sugar dissolves.
Combine the wet ingredients to the sifted flour mixture. Whisk gently until it is lump free. Pour the batter into cupcake liners until 3/4 full.
Steam on high for 15 minutes. (Note: Be careful not to burn yourself when removing the cupcakes from the steamer. I used tongs.) Cool completely before glazing.
Salted Caramel Glaze Instructions
Melt the butter in a large, deep heavy-duty saucepan. Stir in the sugar and and stir until golden brown. (Note: Do this on low to medium heat. The first time I did it, I did it on high and everything burnt. This should take about 10 minutes.)
Take off the heat and pour in half the cream and whisk like a crazy person until the caramel is smooth. Whisk in the rest of the cream and the salt.
Cupcake Assembly
Poke holes in the cupcakes and drizzle copious amounts of the caramel into them.Chill the rest of the caramel in the freezer for about 15 minutes. Once it is thicker, spread the caramel over the cupcakes.
Notes
I got the recipe for this cupcake from Pusiva's Culinary Studio. I have reprinted the recipe below. The only change from the original was to add the fleur de sel. A VERY important point about this recipe is that it did not state how many cupcakes it would make. As it turns out it, it only made 6 cupcakes. Definitely double it if you would like more than 6.I got the salted caramel frosting recipe from Vanilla Garlic. He used it on Apple Cardamom cupcakes which make me drool just looking at them.