1. Peel the pears, cut lengthwise and core. Brush with lemon juice. With a sharp knife make cuts crosswise.
2. Put the pears in a baking sheet, lined with a buttered aluminum foil. Brush the pears with butter and sprinkle with plenty of sugar. Put the baking sheet under the grill for 5 minutes or until the pears are nicely browned.
3. In a saucepan melt 4 1/2 tablespoons sugar, stirring with a wooden spoon until golden. Remove from the heat and add immediately 3 tablespoons of boiling water (it splatters). Add the cream and stir until the caramel is dissolved. Return the saucepan to medium heat, bring to boil and cook until the mixture thickens.
4. Remove from heat, add vanilla to taste and the cold butter. Stir. Serve with the baked pears.