- Whisk egg yolks in a small bowl and set aside.
- In a medium saucepan, combine brown sugar, cornstarch and salt. Stir in milk and cream over medium heat.
- Continue to cook, while stirring constantly until the mixture is simmering and thickened.
- Remove from heat and whisk about a cup of the hot mixture into egg yolks. Return the egg yolk mixture into saucepan and put back over heat.
- Cook while stirring constantly until the mixture is simmering once again. Simmer for a minute while stirring. If you aren't stirring, lumps may form but that can be fixed with a mesh sieve.
- Remove from heat, whisk in the butter and vanilla. Pour into a bowl and let the mixture cool. Press a piece of plastic wrap over the surface of pudding to keep from forming a skin.
- Chill until its time to serve.