Help with coming out to my mom

I just recently accepted I was gay and now want to come out to my mom. I've already came out to my brother and he's very supportive, so that makes it a little easier. But I need some tips of how to strike up a conversation to tell my mom, I know she'll be supportive because she's said on multiple occasions that she doesn't care if I'm gay, and will support me always. But even after she said that I still find myself unable to tell her.