In a small saucepan, heat the heavy whipping cream over medium heat until it bubbles. Remove from heat and add chocolate chips and light corn syrup, letting sit for 5 minutes until softened. Stir until smooth, add butter and salt, let cool slightly.

In a small pot, combine water and granulated sugar, bringing to a boil. Dissolve sugar and whisk in cocoa powder. Cool before storing.

Preheat oven to 350°F (175°C). Line muffin pan with cupcake liners.

In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, and baking soda. In another bowl, combine sour cream, oil, egg, and vanilla. Gradually add wet to dry, stirring until just combined.

Fill each cupcake liner 3/4 full with the batter. Bake for 20-22 minutes or until a toothpick comes out with moist crumbs.

Remove from oven and cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Melt dark chocolate for frosting and let cool. Beat butter until creamy, then mix in cocoa powder, vanilla, and salt. Gradually add powdered sugar and cream until desired consistency.

Poke holes in cooled cupcakes and brush with simple syrup. Remove a small section from the center of each cupcake for ganache. Fill with ganache and frost with buttercream.

Drizzle leftover ganache over the buttercream swirls for a finishing touch.