How to ask girl out at coffee shop

The other day I met this super cute girl who works behind the counter at the coffee shop near me. Another girl was taking my order but the girl this post is about started making conversation with me about my t-shirt and bands I like. I was with a family member and didn't feel comfortable asking her out then.

Realistically, where do I go from here? Call the place and ask when she's working again? Show up another day and hope she's there to pick up our conversation and see if she's interested enough to give me her phone number? If she's not, do I leave a note with one of her coworkers? How do I go about this without looking like a creep/stalker.