Bring milk and cream to a simmer slowly on low heat.
Whisk the sugar and cornstarch together, add the egg yolks, combine well.
Slowly whisk the warm milk into the egg mixture, whisking constantly. Add vanilla. Return to the saucepan and stir gently until thickened. Serve hot, or cool to use as a layer in trifles, or fill tart pans.
Tip. If using it hot, it can be kept warm in a jug set in a pan of hot water with a bit of cling film on top to prevent a skin forming.