In a large pot on medium-low heat, melt the butter.

Add in the celery and leeks, and sauté for 5 minutes.

Add in the coarsely chopped cilantro and poblano peppers. Sauté for an additional 5 minutes.

Add the flour, stir to combine and sauté for 2 to 3 minutes.

Add the chicken stock and stir to combine.

Bring the sauce to a boil, then lower heat and simmer for 30 minutes or until the sauce reaches your preferred consistency.

Remove sauce from the heat and strain out the vegetables. Finely mince about 1/2 cup worth of the vegetables and return only the finely minced vegetables, along with the finely minced cilantro, to the sauce. Stir to combine.

Add a pinch of nutmeg, stir, and serve.