For me, your ratios are a little bit off from what I'm used to and I mix the flour into the yolk/sugar mixture rather than the milk/cream. Here's how I do it:
I use a little higher ratio of yolks to milk/cream, right at four large yolks per cup of milk/cream, about 1/4 cup of sugar per cup of milk/cream, and 1/4 cup of flour per cup of milk/cream
I heat the milk/cream to 180°F or so, generally with a vanilla bean, and meanwhile, whisk the egg yolks with the sugar until pale yellow and thickened, then whisk the flour into the yolk/sugar mixture. Also, 1-2 tablespoons of soft butter per cup of milk/cream
While whisking, temper with about 1/2 of the milk/cream drizzled into the yolk/sugar/flour mixture, then whisk that mixture into the remaining milk/cream in the saucepan and bring to a boil when it will thicken, whisking continuously to avoid scorching. When thick, remove from heat and, after cooling slightly, whisk in the butter and vanilla if you didn't use the vanilla bean.