Butterscotch Pudding Clumps

Excellent butterscotch pudding has been a Holy Grail of mine for forever. I have an idea of exactly what I want, but I've never accomplished it. Either the flavor isn't rich enough, or it's clumpy. This season America's Test Kitchen tackled butterscotch pudding, so I tried it yet again. I really loved the flavor of this recipe, but I had to strain out tiny clumps of egg yolks. ATK promised me that I wouldn't have to do that! ATK's Butterscotch Pudding

This is what they did differently:

Smoother Route to Pudding?

Pudding recipes almost always have you temper the yolks and cornstarch (i.e., add some hot dairy to the mixture to gradually raise its temperature), add everything to the remaining dairy in the pot, and stir constantly as the mixture slowly comes to a boil and thickens. Inevitably, bits of egg still overcook and need to be strained. We wondered if there was a better way.

EXPERIMENT:

We made one batch of pudding the conventional way and a second batch in which the yolks never saw the heat of the stove: We added a little warm milk to the yolks and cornstarch, brought the remaining “dairy” (in our recipe, the butterscotch mixture) to a boil, and then dumped this hot liquid over the egg mixture and whisked briefly as the pudding thickened almost instantly.

RESULTS:

The conventional pudding needed straining, while the “no-cook” custard was utterly smooth and perfectly thickened.

EXPLANATION:

Boiling pudding is overkill. When cornstarch is combined with liquid, it thickens between 144 and 180 degrees, while yolks diluted by liquid coagulate between 180 and 185 degrees—significantly lower temperatures than the boiling point of 212 degrees. Whisking the hot butterscotch mixture into the yolk mixture heated the pudding to about 185 degrees—plenty hot to properly thicken it but not so hot that the yolks overcooked.

DUMP AND STIR

The only thing I can see that that might have been the problem is that I looked away at a critical moment and the base was nearly boiling over when I removed it from the heat to dump it into the egg yolks. So it was a couple of seconds past "climbing the sides of the pan". Could that tiny temperature difference be the problem? Do you have any idea of the temperature difference between "climbing the sides of the pan" and "nearly boiling over" of a dairy/sugar mixture?