Melt butter with 1 tablespoon olive oil in medium pan over medium heat. (thrivinghomeblog.com)
Heat remaining 1 tablespoon olive oil over medium heat and sauté the onion and green pepper 5 - 7 minutes until onion is translucent and beginning to brown. (quakeroats.com)
In large Dutch oven over high heat, brown onion, garlic, celery and bell pepper in remaining tablespoon olive oil until soft (3 minutes). (connoisseurusveg.com)