Step 1In a saucepan, bring the cream and corn syrup to a boil.
Step 2Remove from the heat and add the chocolate and butter. Let stand for a couple of minutes. Whisk until smooth.
Step 1Dissolve the espresso powder in a tablespoon of water, making a paste.
Step 2Place the egg whites and sugar in the metal bowl of an electric mixer. Set it over a pan of simmering water, whisking until the sugar has dissolved (so you don't feel any grains between your fingers). Be careful not to let the egg whites cook at this stage; constant beating is important.
Step 3Remove from the heat. Add the cream of tartar and, with an electric mixer using a whip attachment, beat on high speed until stiff peaks form.
Step 4Add the butter a tablespoon at a time on slow speed. It may look like undercooked scrambled eggs for a while, but just keep beating it on low until it comes together into a smooth buttercream, about 15 minutes.
Step 5Add the espresso paste. If you want a stronger espresso taste, make more paste and add.
Step 1Heat the oven to 350 degrees. Put cupcake liners into mini-muffin tins.
Step 2Sift together the flour, baking soda, baking powder, salt and espresso powder.
Step 3In a bowl, beat the butter and sugar until light and fluffy. Add the eggs slowly, beating well after each addition
Step 4Alternately add the flour mixture and the milk to the butter mixture, about half at a time, mixing slowly. Do not over beat; mix only until well blended.
Step 5Fill each muffin tin three-quarters full.
Step 6Bake 10 to 12 minutes until the cupcakes spring back when you touch them.
Step 7Remove the cupcakes from the pan and cool completely.
Step 8Put a quarter-sized dollop of chocolate ganache in the center of each cupcake, leaving the cake exposed around the edges. (You can use a small teaspoon or a pastry bag; warm the ganache slightly over some simmering water if hardened.)
Step 9Put some espresso buttercream into a pastry bag fitted with a round tip. Start piping at the edge of each cupcake, working in circles to reach the center.