Preheat oven to 375 degrees. Heat 2 tablespoons butter in a large skillet over medium heat; add pears, sugar, lemon juice, and a pinch of salt. Cook over medium heat, stirring frequently, until pears are very soft and most liquid has evaporated, 20 to 25 minutes; remove from heat.
Melt remaining 4 tablespoons butter; set 1 tablespoon aside. Working with one slice at a time, brush butter onto bread, and arrange, buttered side down, along the sides of a 5-to-6-cup ovenproof bowl, overlapping slightly. Cover bottom with a single slice of bread. Reserve remaining bread to cover fruit.
Fill lined bowl with pear mixture, mounding in center (fruit will settle during baking). Cover all with remaining bread slices; trim to fit tightly to edges of bowl. Brush with reserved butter, and press in firmly, sealing edges.
Bake until golden, 20 to 25 minutes. Cool 5 to 10 minutes in pan; turn out onto serving plate. Sift confectioners' sugar over the top. Use two large spoons to divide charlotte into pieces, and serve with lightly whipped cream.