Preheat the oven to 400F. Line a large baking sheet with parchment paper and set aside.
Mix together ground beef, grated onion, minced garlic, salt, pepper, egg, chopped mint and breadcrumbs. Once combined, form into meatballs using about 1 tablespoon per meatball and place spaced apart on the baking sheet.
Bake meatballs for 15 minutes and then turn to low broil for 5 minutes, watch carefully so they don't burn. Set meatballs aside.
For the buns
In a medium skillet, melt the butter over medium heat. The butter will foam up and might spatter a bit. Continue cooking, stirring often, until the butter turns golden brown and the milk solids turn from yellow to chestnut red to brown, 4 to 5 minutes. Immediately transfer to a heat-proof bowl and let cool.
Grease a large bowl with the vegetable oil.
In a large bowl or the bowl of a stand mixer fitted with a dough hook, mix the flour, sugar, yeast, and salt. In a small saucepan, heat the milk until a thermometer registers 120°F - 125°F.
Add the milk to the dry ingredients and stir until mixed. Add the egg and stir to mix well. Knead until a smooth dough forms, 5 to 10 minutes.
Gradually mix in ½ cup of the cooled browned butter. The dough will separate a bit, but keep on mixing and it will come together. Knead until the dough is soft and completely combined. Transfer the dough to the greased bowl and turn to coat. Cover with a tea towel and set in a warm place until doubled in volume, about 1 hour.
Meanwhile, butter a 9x13-inch baking pan with the reserved brown butter.
Transfer the dough to a work surface. Press into an 8x10-inch rectangle. Using a sharp knife, cut the rectangle into 12 equal pieces.
Working with 1 piece at a time, press into about a 3 ½-inch square or round. Sprinkle with 1 rounded tablespoonful of the shredded mozzarella cheese and place one cooled meatball in the middle. Pinch the edges firmly together, then turn over and roll into a ball. Place in the prepared baking dish. Repeat with the remaining dough - you’ll use 12 meatballs so whatever is leftover you can enjoy another time!
Cover the rolls with a tea towel and set in a warm area until doubled in volume, 40 minutes to 1 hour.
Preheat the oven to 350°F and place the oven rack in the bottom third of the oven. In a small bowl, make the egg wash by whisking the egg and milk together. Brush the egg wash generously over the tops and sides of the rolls. Mix together the hemp hearts and sesame seeds and sprinkle over the rolls.
Bake the rolls on the rack in the bottom third of the oven until deep golden brown, about 15-20 minutes. Transfer the pan to a rack.
Make the garlic butter by melting the butter with the minced garlic, once the butter is melted, cook for 1-2 minutes until the garlic is fragrant. Remove from the heat and stir in the parsley. Immediately brush over the buns and sprinkle with flaky sea salt.
Let cool in the pan for 10 minutes. While the buns cool, warm the marinara sauce in a small pot over medium-low heat.After 10 minutes, serve the buns with the warm marinara sauce for dipping.
Video
Notes
Serve these cheesy meatball stuffed buns as a fun appetizer!
Or, make this into a main dish by serving with one of our delicious salads as a side -