Melt the butter in a medium pot over medium-high heat, add in onion and and sauté for 2-3 minutes, stirring often until the onions begin to wilt.
Sprinkle in the flour remove from the heat and stir or whisk until combined.
Return to the heat and cook for a minute more, stirring constantly.
Slowly add in the chicken stock, ⅓ of it at a time, stirring constantly and scraping up any browned bits from the pan. The filling will begin to thicken just after it begins to bubble.
If adding potatoes do so here and allow them to simmer for 5 minutes.
Add in carrots and peas.
Sprinkle in the chicken bullion and truffle salt (if using) and stir to combine.
Simmer for 5 minutes.
Remove from heat, add in your heavy cream, stir, place back on heat and allow it to just start to simmer.
Add in shredded cooked chicken, stir. Taste and adjust seasoning.
Remove from heat and allow it to sit for a few minutes.
Serve with biscuits, pie crust cut outs, crescent rolls or bread.