Melt butter in a stock pot over medium-high heat; sauté onions, celery and garlic ~6 minutes, until translucent and tender.
Add flour, stir, cooking one minute.
Stir in chicken broth; half & half, salt and pepper.
Bring to a bubbly boil; reduce heat to low; simmer, uncovered, ~15 minutes.
Transfer all to a food processor; purée; return to warm stock pot; heat through.