Preheat oven to 400°. Melt butter over medium heat in a large sauté pan. Add shallot, celery, and garlic, and sauté 8 minutes or until vegetables begin to soften; transfer to a large bowl. Add olive oil to skillet, and heat over medium-high heat 1 to 2 minutes or until hot. Add fennel, and sauté over medium-high heat 8 to 10 minutes or until lightly browned.
Add fennel to celery mixture; let cool 10 minutes. Stir in remaining ingredients until well combined. Spoon into a lightly greased 13- x 9-inch baking pan. Bake at 400° for 40 to 45 minutes or until lightly browned. Let stand 10 minutes before serving. Garnish, if desired.