She might be Turkish if you're in Germany.

Situations like this are blisteringly simple. Before you get to the counter take a deep breat, relax; then, let her ring up your order, hand over the money and get the reciet. Her job is done, now you say:

"So, do you fancy going out for a drink later this week?"

Don't bother with any of the "building a relationship", you can't because she's doing her job, at best you'll come off as "sweet", at worst stalkerish.

Remember, money reciet, then ask. Whatever the hell you do don't ask before you hand over the money.