This is common problem for guys. The reason you can't create a more sexual interaction is because you are "blocking" the sexual energy. The main reason for that is usually (sexual) shame. It's a very subtle but incredibel destructive emotion. You might have learned some where during your growing up that you should be ashamed to your desire as a man.
Unfortunately it's not the easiest pattern to get rid of. What i suggest is to become present with your desires. Feel them,and don't block them. Daily meditation really helps with this. The second step would be to "express' your deisre (not necessarily in logical direct way). when you don't have the shame and are in touch with your desire for her THIS is what creates sexual interest in her. It doesn't matter if the conversation if small talk or not. You can give her sexually tinted hints, do some teasing. Touching is also very important. This all happens naturally when you are in touch with your masculine energy (your desire).
Hope that wasn't too vague
. question welcome.Ivan