Love the technique of making a 'raft ' for clarification.
Roughly cut the vegetables and put into robot coup (for processor) with peppercorns, bay leaf parsley stems and thyme. Blend until fine.
Add the lean mince to the vegetable and herbs and blend.
Remove the meat, vegetable and herbs to a bowl and add the egg whites. mix until unified. This is the 'clarification'.
Put the cold stock on a low heat and add the clarification. Stir until it reaches 60 degrees celsius - this prevents the protein from sticking to the bottom.
Allow the liquid to come to a low simmer and DON'T STIR. The clarification will coagulate and rise to the top and any impurities in the stock will be trapped in what is called 'the raft'
Gently simmer for 1 - 2 hrs
Using a ladle carefully remove the liquid without breaking the raft and pass through a chinois lined with muslin or a filter paper.
Remove any fat. This can be by allowing to cool and lifting off any fat or dabbing liquid with absorbent paper.
Taste and adjust seasoning - serve in appropriate bowl with garnish of choice.