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1
Adjust oven rack to middle position and heat oven to 475 degrees.
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2
Place wire rack in foil-lined rimmed baking sheet.
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3
Mash bread, 1/2 cup broth, and 1/2 cup sour cream into paste in large bowl using fork.
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4
Mix in ground beef, egg yolks, 1 tsp salt, 1/2 tsp pepper, allspice, nutmeg using hands.
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5
Pinch off and roll mixture into tablespoon-size meatballs (about 60 meatballs total) and arrange on prepared baking sheet.
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6
Bake until lightly browned, about 15 minutes.
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7
Transfer meatballs to slow cooker, discarding rendered fat.
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8
Melt butter in a 12-inch skillet over med-high heat.
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9
Add onions and cook until softened and lightly browned, 8-10 minutes.
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10
Stir in flour and cook for 1 minute.
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11
Slowly whisk in remaining 2 1/2 cups broth and soy sauce, scraping up any browned bits and smoothing out any lumps.
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12
Pour mixture over meatballs, cover, and cook until meatballs are tender, 4-6 hours on LOW.
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13
Let meatballs and sauce settle for 5 minutes, then remove fat from surface using large spoon.
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14
In bowl, combine 1 cup hot cooking liquid with remaining 1/2 cup sour cream (to temper), then gently stir mixture into meatballs.
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15
Gently stir in dill, season with salt and pepper to taste and serve.
