In a small saucepan, heat heavy whipping cream over medium heat until bubbling. Remove from heat and pour over chocolate chips and corn syrup; let sit for 5 minutes. Stir in butter and a pinch of salt until smooth. Let cool to room temperature.

In a medium saucepan, combine water, granulated sugar, and cocoa powder. Bring to boil over medium heat, stirring until dissolved. Cool to create simple syrup.

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

In a mixing bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt.

In another bowl, mix warm water, sour cream, vegetable oil, egg, and vanilla extract until combined.

Pour wet mixture into dry ingredients and stir until just combined. Do not overmix.

Fill each cupcake liner ¾ full with batter and bake for 20-22 minutes. Check with toothpick for doneness.

After baking, let cool in the pan for 10 minutes then transfer to a wire rack to cool completely.

For frosting, melt dark chocolate and beat together butter until creamy. Add cocoa powder, vanilla, and salt, then gradually mix in powdered sugar and cream to desired consistency.

Poke holes in each cooled cupcake and brush with simple syrup. Fill centers with ganache, replace tops, and frost with chocolate buttercream. Drizzle with remaining ganache.