In a medium sized saucepan on low heat, warm the milk just until it barely simmers.
Meanwhile, whisk together the egg yolks and sugar in a medium sized bowl until they are thickened and light colored - about 1 minute. Sprinkle the flour over the top of the mixture and whisk to combine.
Remove the milk from the heat and gradually add it to the egg mixture, whisking all the while to keep the egg yolks from coagulating into clumps. Pour the mixture back into the saucepan.
Place the saucepan on low to medium heat and heat until it just boils, stirring gently the whole time. Take care in particular that the bottom edges do not scorch. The mixture will thicken and the whole process takes about three minutes on medium heat. Don't stop stirring or you may get clumps and/or burn the cream. Whisk vigorously if clumps do start to form.
Remove the mixture from the heat and stir in the vanilla extract. Scrape the cream into a bowl where it will cool. After it has cooled a little, cover the surface with a piece of plastic wrap and place it in the refrigerator to cool completely. The plastic wrap helps prevent a skin from forming.