A question about a recipe: Madeira Tart

I have a question about step 1 on the recipe "Madeira Tart" from thirschfeld. We should cover the custard with plastic wrap to avoid a skin forming, right? It says:

"For the custard: Place the milk into a sauce pan and scald it over medium high heat. Remove the pan from the burner. In a mixing bowl whisk together the eggs, sugar, madeira and salt. Temper the eggs by whisking in a 1/2 cup of warm milk and then add the rest while whisking. Cover the bowl and place the custard base into the fridge. You want it to be cold. It can sit in the fridge overnight, which is probably best, but at least let it get to 35 or so degrees F. You could do this in an ice bath if you are in a hurry."