Heat oven to 350°F. Prepare two muffin pans with cupcake liners.
Stir together sugar, flour, cocoa, baking powder, baking soda and salt in large bowl.
In a second bowl, whisk together eggs, oil, vanilla, sour cream, and sugar.
Add dry ingredients to wet ingredients, mixing just until combined. Fill each cupcake well with 2/3 batter.
Bake for 12-14 minutes, until wooden pick inserted in center comes out clean, rotating pans halfway through baking. Remove cupcakes from pans and allow to cool on a wire rack. Cool completely.
For the 7-minute icing, in a medium-sized saucepan combine the water, sugar, egg whites, cream of tartar, and salt.
Using an electric mixer set on low, beat the egg white mixture for 30 seconds. Set the bowl over the saucepan of simmering water. Be sure the bottom of the bowl does not touch the simmering water. Continue beating at high speed for about 7 minutes, or until the egg whites are stiff and glossy.
Remove from the heat, and add the vanilla and beat for an additional 2-3 minutes until bowl feels cool to the touch. Use frosting right away as it tends to set quickly.
To fill the cupcakes: use the cone method by cutting out the center out of the cupcake at an angle about two-thirds of the way down. Save the top of the cupcake and simply trim off the bottom so you can replace the top of the cupcake once you have filled them with the marshmallow creme. Using a piping bag or a Ziploc bag with a corner snipped off, fill the center of each cupcake with the marshmallow creme. Just be sure not to overfill. If you fill above the cupcake, simply use a small spatula to scrape off the top. Place the trimmed top that you saved back on the cupcake. You will need some of this icing to pip swirls on top.
To make the ganache: Cook the chocolate chip and heavy cream over a double boiler over simmering water until smooth and warm, stirring occasionally. Allow to cool slightly, then dip the top of each cupcake into the ganache so that ganache covers all the way to the liner. Allow any excess to drip off. Place each one back onto the cooling rack.
Use remaining white icing to pipe swirls on top of cupcake.