Preheat the oven to 325 degrees F. Line 30 regular-size cupcake or muffin cups with paper cupcake liners or line 6 dozen (72) mini cupcake or mini muffin cups with mini cupcake liners.
In a mixing bowl, combine the flour, baking soda, and salt. Sift the cocoa powder in a separate bowl. Whisk the hot water into the cocoa until smooth. In bowl of electric mixer, cream the sugar and butter well. Add the eggs, buttermilk, oil, and vanilla and mix until smooth. Add the dry ingredients to the wet ingredients and add the cocoa mixture. Beat just until smooth. Fill the cupcake liners 3/4-full and bake the regular-size cupcakes for 20 minutes, or until cooked through or bake the mini cupcakes for 19 minutes, or until cooked through. Remove the cupcakes from the pan and let cool completely. Fill with Caramel Cream Center and top with Ganache Frosting and the prepared blue rock sugar.
Caramel Cream Center:
Warm the egg whites and sugar over a double boiler, stirring the egg mixture until the sugar dissolves and the mixture feels warm to the touch. Remove from the heat and whip until medium-stiff peaks form. With the mixer running, gradually add the softened butter and vanilla until thick and smooth. Fold in the Agave Caramel Sauce until fully incorporated. Place the Caramel Cream Center in a pastry bag fitted with pastry tip and fill the cooled cupcakes.
Agave Caramel Sauce:
In a small saucepan, heat the water over high heat until hot but not boiling. Add the sugar and the agave and stir gently to dissolve. Bring the mixture to a boil, and heat to 330 degrees F, or to a warm brown color. Add the cream slowly, whisking constantly, the caramel will bubble and rise. Add the butter and continue whisking over the heat until the caramel is smooth. Remove from the heat and stir in the vanilla extract. Chill the mixture to thicken.
In a saucepan, heat the cream to scald. Add the chocolate chips. Stir the mixture until smooth. Chill on the ice bath until a spreadable consistency, stirring frequently. Frost the filled cupcakes with the ganache and garnish with the prepared rock sugar.
The yield for the Caramel Cream Center is more than needed. The extra can be used as frosting or frozen for up to 3 months. Thaw at room temperature and stir, before using.