For soup: Melt butter in a medium saucepan. Add onions. Stir over medium-low heat about 8 minutes until soft, do not brown. Add sunchokes and 3 cups sparkling water. Bring to a simmer and cook with vented lid until sunchokes are tender, about 15 minutes. Add pears and cook about 4 minutes until softened. Puree soup in a blender or food processor. Add additional sparkling water as needed for desired consistency. Season to taste with salt and pepper.

While soup is cooking, prepare garnish: Cook bacon with butter in a skillet over medium heat until some of the fat is rendered but bacon is still soft. Bacon should not crisp. Add mushrooms and cook until their liquid is released, 4-5 minutes. Add shallots; cook over low heat until shallots are softened and flavors are melded, about 15 minutes. Makes about ¾ cup.

To serve: Place 2 heaping tablespoons mushroom garnish in a shallow bowl. Pour hot soup over and serve immediately.