Preheat oven to 350 degrees F.
Place baking rack in center of oven , line 12 muffin cups with cupcake papers.
Into medium bowl,sift together the flour,cocoa powder,baking soda and salt.
Gently wisk the dry ingredients together until blended;set aside.
In a heavy-duty electric mixer using the paddle attachment, beat the butter with the sugar at medium speed until thoroughly blended, about 2 minutes.
Beat in the egg and vanilla;scrape down the sides of the bowl with a spatula and beat for 1 minute,until well blended.
Beat in the chocolate. At low speed,beat in the buttermilk one-third at a time,alternating it with the dry ingredients.
Mix just until blended,scraping down the side of the bowl as necessary.
Divide the batter among the prepared muffin cups and bake the cupcakes for 25-30 minutes,until they spring back back when lightly touched.
Cool cupcakes in the pan for 5 minutes,then remove to a wire rack and cool completely.
Making the white chocoalate filling: Place the white cho colate in a stainless steel bowl,In a saucepan,bring the heavy cream to a gentle boil.
Remove the pan from the heat and pour the hot cream over the whitechocolate.
Let the mixture stand for 30 minutes to melt the chocolate:whisk until completely smooth.
Cover the bowl and refrigerate the filling for at least 4 hours,until Well chilled.
Using a hand-held electric mixer,whip the chilled white chocolate mixture until it reaches the consistency of sour cream.
With a small knife,cut a cone shaped peice,3/4 inch in diameter,from the center of each cupcake.
Remove the the cone shaped piece of cupcake,and cut off the bottom of each cone,leaving a round cap for each cupcake.
