Season chicken with salt and pepper; dredge lightly in flour.
Heat oil in a sauate pan pver medium-high heat. Add chicken and brown on all sides; remove. Pour off all but 1 T. drippings and return pan to heat.
Saute leeks, carrots, and mushrooms for 3 minutes. Stir in tomato paste and garlic; saute 2 minutes, stirring often.
Deglaze pan with wine and reduce for 3 minutes; add broth and thyme. Return browned chicken to pan and bring to a boil. Cover, reduce heat to medium-low and simmer 20 minutes.
Stir in butter until melted, then season with salt and pepper. Remove and discard thyme spring.
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