Degrees? Fahrenheit? Yes, you read right, friends. This custard is baked at an insanely hot 425. That’s almost unheard of for a custard, hence all the folks who emailed me last night to make sure I wasn’t drunk. Why are custards usually baked low? Of course to keep the egg proteins from clenching up and curdling the whole works. The rule of thumb is normally to avoid a rapid heating, lest the top of the custard break before the center sets up. This is why crème brûlée is usually baked at about 300.
In this case there are safeguards. First, the bain marie (the water bath). It not only keeps most of the custard insulated around the outside, it cools the pan via constant evaporation. What keeps the top from curdling? The toast of course, and in fact keeping the toast toasty is the reason the oven is set to 425 in the first place. I won’t lie to you, when you make this dish you’ll probably get a small amount of surface curdling between the slices. However the overall effect is well worth these few cosmetic defects.