Preheat oven to 375 degrees F. Let piecrust stand according to package directions.
In a 12-inch skillet heat butter over medium heat; add onion, leek, shallots, sugar, nutmeg, pepper, and 34 teaspoon salt. Cook about 8 minutes or until tender but not browned, stirring occasionally. Reduce heat. Stir in cream cheese until melted. Stir in Swiss and Monterey Jack cheeses until combined.
In a large bowl combine eggs and cream. Gradually stir in onion mixture until combined. Ease piecrust into 9-inch pie plate; pour onion mixture into piecrust. Fold edge of crust over filling, pleating as necessary. Bake, uncovered, about 40 minutes or until crust and top are golden brown and a knife inserted near center comes out clean. Cool on a wire rack for 15 to 20 minutes. Cut in 16 wedges. Serve warm. Makes 16 appetizer servings.