In a small saucepan, combine the brown sugar and cornstarch.

Add milk and egg yolks, stir until smooth.

Cook and stir over medium heat until mixture comes to a boil. Cook and stire 1-2 minutes longer or until thickened.

Remove from the heat and stir in butter and vanilla.

Cool to room temperature, stirring several times. Pour into 4 individual dessert dishes.

Cover and refrigerate for 1-2 hours or until chilled.