Reduce the heat to medium, and melt the remaining butter in the pan. Stir in the garlic, and onion, and cook for 2 minutes, stirring constantly until the onion has begun to soften. Stir in the flour, and continue cooking 5 minutes more. Add the vodka, and bring to a simmer over medium-high heat, stirring constantly. Allow to simmer for 2 minutes, then stir in the tomato paste, chicken broth, salt, pepper, parsley, sour cream, and feta cheese. Reduce heat to medium-low, and simmer 20 to 30 minutes stirring frequently.