Preheat the oven to 350 degrees F. Spray the bottoms 24 the cupcake molds with nonstick spray. Fill each with a double layer of cupcake papers. Alternatively, use a nonstick cupcake tin and spray the sides and bottoms with nonstick spray. Set aside.
In the bowl of a stand mixer fitted with a whisk attachment, "cream" together the butter and granulated sugar until smooth, 3 to 5 minutes. Scrape down the sides with a rubber spatula and mix to blend. Add the brown sugar and continue mixing until both sugars are fully integrated and the butter soft, 3 to 5 additional minutes. With the mixer on a slow speed, add the eggs, 1 at a time.
In a medium bowl, sift together the flour, cocoa powder, baking powder, salt and cinnamon. With the mixer still on low speed, gradually incorporate about half of the flour mixture. When fully mixed, add half of the yogurt. Add the remaining flour and the remaining yogurt. The batter will be fairly dense and thick. Fill the tins a little more than 3/4 full. For a mold that has between 3 and 4-ounce holes, I like to use a 1/3 cup measure, leveled, to fill each one with the same amount of batter. When the tray(s) are full, tap the tray a few times on a flat surface to level the batter out and put the tray(s) in the center of the oven.
Bake for 8 minutes then rotate the cupcakes halfway. Bake for an additional 10 minutes. A cake tester, when inserted into the center of a cupcake, should emerge clean. Remove the cupcakes from the oven and allow them to cool for 5 minutes. Gingerly remove them from the tins so the heat from it doesn't continue to cook the cupcakes and risk drying them out. Set aside to cool completely.
In a small, heatproof bowl, melt the chocolate over a pot of simmering water (a double boiler). In a small saucepan, gently heat the sour cream over low heat. When the cream begins to simmer, shut off the heat and whisk in the vanilla. Use the tablespoon measure to measure out the cocoa powder and add it to the sour cream. Whisk to blend. Without cleaning the spoon, measure the corn syrup and add it to the chocolate. The layer of cocoa powder on the spoon will prevent the corn syrup from clinging to the spoon making it easier to add the precise amount of syrup. When the chocolate has melted, remove from the heat and allow the cream and chocolate to "rest" for 5 minutes. Gently stir them together and set aside.
When the cupcakes are cooled, spread the chocolate glaze over the tops and serve.
Recipe courtesy of Alex Guarnaschelli