1 Sauté grated onion: Melt the butter in a sauté pan on medium-high heat. Stir in the grated onion and cook until translucent and softened, 3-4 minutes. Set aside to cool.
2 Soak bread in milk, shred: Place the pieces of bread in a large bowl and mix with the milk. Let sit for 15 to 20 minutes for the bread to absorb all of the milk. Once the bread has soaked up the milk put the bread in a food processor and pulse until it has been completely broken up (or shred by hand). Return the pulverized milk soaked bread to the bowl.
3 Make meatball mixture with bread, onions, eggs, meat, spices: Stir the cooled onions into the milk bread mixture. Add the eggs, ground pork and beef, salt, pepper, nutmeg, and cardamom. Use your (clean) hands to mix everything together until well combined.
4 Form meatballs: Use your hands to form the meatballs about an inch-thick and place them on a plate or sheet pan. This recipe should make between 40 and 50 meatballs.
5 Brown meatballs on all sides: Heat 6 Tbsp of butter in a large sauté pan on medium heat. When the butter is melted and foamy, start adding some meatballs to the pan.
Working in batches as to not crowd the pan, slowly brown the meatballs on all sides. Handle the meatballs gently so they do not break apart as you turn them.
Once the meatballs have browned on all sides, remove them from the pan and set aside. You do not need to cook the meatballs all the way through at this point, you only need to brown them. You’ll finish cooking the meatballs in the sauce later.
Once you have removed the meatballs from the pan, keep the remaining butter in the pan. You’ll use this butter to make the sauce.
If the butter in the pan has become burnt through the browning of the meatballs, remove and discard it, and add 6 Tbsp of fresh butter to the pan. Otherwise use the existing pan butter, you should have 6 Tbsp total of butter in the pan. If not add more.
6 Add flour to butter in pan to make roux: To make the sauce, first make the roux. Heat the butter in the pan on medium heat. Slowly whisk in the flour. Stir until smooth. Continue to stir, allowing the flour mixture to cook, several minutes, until the roux is the color of coffee-with-cream.
7 Add stock to roux to make sauce: When the roux has cooked to a lovely shade of light brown, slowly add the stock to the roux, stirring as you add the stock.
The stock will sputter at first and the roux may seize up, but keep adding the stock slowly and keep stirring. Eventually the sauce will loosen and become silky.
8 Add meatballs to sauce: Return the meatballs to the pan with the sauce and lower the heat to low. Cover the pot and cook on low heat for 10 minutes. You may need to work in batches.
9 Stir in sour cream and jelly: Transfer the meatballs to a serving dish to serve. Stir in the sour cream. Either stir the jelly into the sauce or serve it on the side.