Preheat oven to 400 degrees F (200 degrees C). Grease 12 muffin cups.
Heat semisweet chocolate and butter together in a saucepan over low heat until melted, 3 to 5 minutes.
Remove from heat and cool for about 10 minutes. Lightly beat eggs into cooled chocolate mixture.
Whisk chocolate-butter mixture, buttermilk, sugar, sour cream, and vanilla extract together in a bowl.
Mix flour, baking soda, and salt in a large bowl; form a well in the center of the flour mixture. Stir chocolate mixture into flour mixture until just combined. Fold chocolate chips into batter. Spoon batter into the prepared muffin cups.
Bake in the preheated oven until a toothpick inserted in the center of a muffin comes out clean, about 18 minutes.
