Chocolate Cupcakes with Peanut Butter Filling

3/4 cup plus 2 tablespoons of cocoa powder
1/2 cup of boiling water (you may need extra water)
1 cup buttermilk
1-3/4 cups all-purpose flour
1-1/4 teaspoons baking soda
1/4 teaspoon baking powder
1/4 teaspoon salt
1-1/2 sticks plus 3 tablespoons unsalted butter, softened
1-1/4 cups granulated sugar (the original recipe calls for 1-1/2 cups)
1 tablespoon instant espresso powder
2 large eggs, at room temperature
1 teaspoon pure vanilla extract
1 cup peanut butter (smooth)
2/3 cup icing sugar
1 cup heavy cream
8 ounces semisweet chocolate chips (I used mini chips -- the original recipe calls for chopped semisweet chocolate)
Preheat the oven to 350 degrees F.
Line 24 muffin cups with cupcake liners. If you don't have liners, be sure to butter your muffin tin(s) well.
Put the cocoa powder in a bowl and add the boiling water. Mix until a smooth paste forms. You may have to add more than 1/2 a cup of boiling water to form a paste.
Once the paste is formed, whisk in the buttermilk.
In a separate bowl, sift together the flour, baking soda, baking powder and salt.
In a large bowl, begin creaming 1-1/2 sticks of butter with the sugar. Cream until light and fluffy (3 to 4 minutes).
Beat in the eggs and vanilla until well combined (be sure to stop and scrape down the sides of the bowl).
Add half the dry ingredients to the butter/egg mixture. Mix well.
Add half of the cocoa mixture. Mix well.
Add the rest of the dry ingredients. Mix well and then add the remaining cocoa mixture and mix well.
Spoon the batter into the prepared muffin tin(s).
Bake for 20 to 25 minutes, or until the cupcakes spring back when touched lightly. Cool the cupcakes in the pan for 10 minutes and then transfer them to wire racks to cool completely.
In a bowl, beat the peanut butter with the remaining 3 tablespoons of butter. Sift in the icing sugar and beat for about 2 minutes. The mixture should be light and fluffy. Spoon the mixture into a pastry bag fitted with a 1/4-inch star tip.
Pick up a cupcake and press the tip of the pastry bag into the cupcake (not more than an inch into the cupcake). Gently squeeze in some filling and pull the tip out. You will feel the cupcake expand as you inject the filling. Fill all the cupcakes.
In a saucepan, bring the heavy cream to a simmer. Remove from heat and add the chocolate. Let it stand for 5 minutes and then whisk until you have a smooth chocolate icing (try not to eat it all with a spoon!). Let the icing stand for about 15 minutes; it will thicken a bit.
Gently dip the tops of the cupcakes into the icing using my "dip n' twirl" technique. Just lower the cupcake top into the icing and twirl gently. While the original recipe recommends dipping once, waiting 5 minutes and then dipping again, I only dipped once.
Let the cupcakes sit for about 1/2 an hour and then pipe rosettes onto the cupcakes using the remaining peanut butter filling.