Preheat oven to 350°F.
Melt the butter in a heavy-bottomed pan. When almost completely melted, stir in 4 oz. of chocolate. Let soften for a moment, then remove pan from heat and stir with a wooden spoon until the butter and chocolate are smooth and melted.
Add cherry jam, sugar, salt, and eggs to the chocolate mixture until combined, then stir in the flour.
Pour batter evenly into a 12-cup muffin pan lined with paper cups. Bake for 25 minutes. Cool in pan on a rack for 10 minutes before turning out. Allow to cool completely before icing.
When the cupcakes are cool, heat the heavy cream until boiling, then remove pan from heat and add the chocolate, quickly stirring to melt and incorporate. For a more elevated look, allow the icing to cool, then whip until thick and smooth. Pipe onto each cupcake before nestling a cherry in the center.