Caramelize 1/2 cup sugar with 3 tablespoons butter. Pour out the caramel into a buttered and lightly floured tray and arrange slices of pears on top, after it cools a bit.
Beat the remaining butter and 1 cup sugar well, and add the yolks one at a time, as well as the milk. Add the mixed baking powder, flour and vanilla. Beat well and using a wooden spoon, add the egg whites that you've beaten into snow.
Pour the cake mixture into the tray with the pears and bake until ready in a moderately preheated oven (about 45-50 minutes). Allow it to sit for 20 minutes in the tray to cool, and invert it onto a platter.