Grease a 12-cup muffin pan and coat the cups with sesame seeds. Warm the water and melt the butter in it.
Cook the onion and ground beef in the oil until the beef is crumbly. Stir in tomato paste, ketchup, mustard, pickle brine, salt, and pepper, then cool slightly.
Combine flour, crumbled yeast, salt, sugar, and the warm water-butter mixture. Knead for about 5 minutes, cover, and let rise until visibly enlarged.
Preheat the oven to 400°F. Divide the dough into 12 pieces, roll each into a 4-inch round, press into the muffin cups, and divide the beef filling among them.
Bake for about 15 minutes. Top each muffin with cheese and return to the oven for about 3 minutes, until melted.
Remove the muffins from the pan and top each with pickle slices, ketchup, and chives. Serve warm.
Notes
Recipe facts translated and extracted from the first specific recipe linked by the claimed Oetker finger-food source page.