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1
Heat 25gr of the butter on a low heat, and add the sliced onions and cook for 5 minutes, then add a few tablespoons of the stock.
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2
Cook this for 10 minutes watching it doesn't burn and then add half the stock and cook again for another 10 minutes and add one third of the milk.
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3
Allow to cool slightly and puree in a blender or processor.
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4
Return to the pan with the remaining stock.
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5
Prepare the cheese balls ~ Melt the butter in a pan, stir in the flour, mix well with a wooden spoon, add 225ml of hot milk and stir until the mixture is thick and smooth.
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6
Season with salt, pepper and nutmeg.
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7
Remove from heat and beat in the egg yolk and Gruyere cheese.
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8
Mix well and turn the mixture onto a damp plate and cool completely.
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9
Divide into small even portions and form lots of tiny balls about 2cm (3/4 inch) across.
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10
When formed roll the balls in extra flour.
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11
Add the remaining milk to the onion soup and bring to the boil.
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12
Drop in cheese balls.
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13
Cook for 5 minutes and remove carefully with a slotted spoon and divide evenly amongst soup bowls, then cover with remaining soup.
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14
Serve.
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15
Sprinkle with chopped parsley if desired.
