Combine 1 cup sugar, flour, and salt in a medium saucepan; add milk and egg yolks, stirring until smooth. Cook over medium heat, stirring constantly, until mixture is thickened and bubbly. Remove from heat, and set aside.
Sprinkle remaining sugar evenly in a 10-inch cast-iron skillet. Cook over medium heat, stirring constantly with a wooden spoon until sugar caramelizes. Remove from heat, and carefully pour into warm cream mixture. Stir until smooth.
Pour caramel mixture into pastry shell; chill completely. Serve with dollops of whipped cream.