update: I tried these with chocolate chips and tasted the batter, and it definitely needed a lot more sugar added (1/2 cup? no idea, I just poured until the batter was delicious) plus some cinnamon. then it was good.
I really like the idea of finding creative ways to use up leftovers like breadcrumbs so this was a fun experiment. My crumbs were from commercial 100% whole wheat bread and of course the results would vary depending on the type used. I find commercial bread saltier than homemade and would omit the salt next time. Also, mine did not rise very much and had a spongy texture. They were better straight from the oven than after sitting awhile. A good dinner muffin, possibly with some herbs added. Like ladypit writes, this is a base recipe. I will make them again and fiddle with the ingredients to come up with some other variations. Thanks, ladypit, for posting!