"To make the custard" means preparing a creamy and sweet dessert sauce by mixing eggs, milk (or cream), and sugar together and heating it until it thickens. Full definition
This vegan recipe looks so much easier than making a custard base > < and probably tastes just as good! (faring-well.com)
Start by making the custard, as it will need to cool while you work on the other steps. (outside-oslo.com)
Meanwhile, in a mixing bowl whisk together sour cream, egg, egg yolk, light cream, fresh thyme, parsley and salt and pepper to make the custard filling. (theartfulgourmet.com)