To stem a jalapeño

I made some tomatillo sauce today. This recipe is known to be a little spicy, but the sauce wound up being palate-scorching. Turns out when I read "2 jalapeños, stemmed", I took that to mean "cut off the stem" when in reality it also means "cut out the seeds and membranes while you're at it". Whoops. A few teaspoons of sugar calmed it down a bit, but that was still probably the spiciest burrito I've ever eaten.