I've only made homemade chili rellenos once or twice -- not sure which of the recipes I used (no notes kept then . . . as I do now).
HUGE amount of work, plus the grease smell in house for days (no exahust fan in kitchen, only "recirc").
Do you have an Uncle Julio's or a Chevy's near? Both of those have rellenos on the menu. They are what I would call semi-authentic.
A REAL one will have Mexican cheese inside the chili pepper -- usually queso blanco I think.
And the red sauce will be fairly hot but clear/smooth (not chunky). Some sauces are simply onion, tomato, and ckn broth. Others are more complex with seasonings -- chili powder/cayene to taste.
The batter should be not-too-thick. (If it's like the thickness of a twinkie, it's too much --
) In my batter I add a pinch of freshly ground roasted cumin (roast the cumin in toaster oven or frying pan) -- then use mortar and pestle to grind or mini-mincer/coffee grinder.
HOT fat so that the frying is quick and the result isn't a grease sponge (ahem, Twinkie).
Great rellenos are fantastic.
Oh yeah, and I oven roast my own peppers first -- then pull off the charred skin & remove most seeds (leaving some seeds will leave more heat) . . . so, more time there too.