Preheat oven to 475 degrees F (245 degrees C). Butter and flour a large 4-cup muffin tin.
Melt butter and semisweet chocolate in a small saucepan over low heat; stir until smooth and shiny, about 3 minutes.
Mix 1/3 cup plus 1 tablespoon sugar and flour together in a bowl. Add eggs 1 at a time. Add butter-chocolate mixture gradually; stir until well combined. Pour evenly into the prepared muffin cups; add a candy kiss in the center of each one, making sure it is covered by the chocolate mixture.
Bake in the preheated oven until mostly set but still runny in the center, about 10 minutes. Allow to cool before eating, about 10 minutes.
