How do you respond to a work acquaintance who never orders anything (despite constantly saying she is going to) but constantly asks you to bring her free desserts?  It's getting kind of uncomfortable.

i'd smile and say "no" --

but if you are bringing them stop -- and don't discuss your work with her or when she's around

Haha!  I thought exactly the same thing, NO.  Say no, then ask her to bring you lunch for the next day.

Stop bringing them. When she ask give a condescending laugh, and say yeah right

I'd be a little more blunt and say something like "I can't afford to keep bringing in these free desserts but if you want to buy something I'll be glad to make it for you"  She is really taking advantage of you.   

Yeah.  I agree with everyone else.  Just be honest.  "I'm flattered that you like my work, but it takes time and money and I have to invest my samples where I get a return on my investment, but I'm just so flattered you like my recipes.  What is your favorite thing to make?"  It redirects it back at them, thanks them, and is kind.  If it continues you can pretend she's joking and laugh, but not in a mean way, until she stops.  

No. Short. Sweet. I'd even smile, but no.

Or, next time she asks you to bring something, pretend you didn't hear the word "free" or "bring me the extras".  Tell her you are excited she is finally able to place an actual order and tell her the price. She'll probably never ask for free dessert again.