Heat butter in a large Dutch oven over medium-high heat until bubbly. Add shallots and garlic; cook 3 minutes or until soft. Add spinach, and cook 5 minutes or until spinach is wilted and liquid has mostly evaporated. Place spinach in a colander, pressing leaves to remove any excess liquid; cool slightly. Divide spinach, artichokes, and cheeses among 8 lightly greased 1-cup ramekins (or place in a 2-quart baking dish). Combine eggs and next 4 ingredients in a large bowl; pour egg mixture over spinach mixture. Cover and refrigerate 8 hours or overnight. Preheat oven to 350°. Bake, uncovered, 45 minutes or until centers are just set. Let stand 5 minutes before serving. Garnish, if desired.