It looks like this

I wouldn't stress it now by cutting off anything. When it gets healthy leaves I would give it a very diluted fertilizer. According to Rodale's compost book, coffee grounds have very little nutrient content.

Do you grow potatoes? If you do, treat it as you would a potato you want to grow as a crop.

If you don't grow potatoes: make sure the tuber has excellent drainage, and is watered only when the top of the mix is dry about 2-3cm down. Not too much at all. Maybe half a cup a week until there are more leaves to use the moisture.

You can feed it with dilute tomato food.

When you come to plant it out in the yard be sure that you've dug the ground well, put in compost at least three weeks before, plus a stake in the site - and the plant will get at least eight hours of sun a day, plus wind shelter if it is a tall variety.

If this sprout doesn't make it, be slow to panic. There may be other sprouts to follow.

If you suspect Bad Things have happened - tip it all out and check for mushy tuber/black and flabby roots. If it hasn't gone too far - scrape out the mush, leave the tuber to dry until the wound has scabbed over and replant in a much smaller pot that will dry out much faster. Water cautiously until new shoots arise.

If this happens it can take two years or so to reach flowering. I suggest it for the 'just in case' scenario and if it is a plant you cherish because of who gave it to you.

I agree, there is a lot of energy stored in dahlia tubers and it will probably put up more stems if that one dies. I've broken plenty of stems clean off while starting them indoors and there were always more later. Make sure it gets as much light as possible thru the window, and maybe even start putting it outside on warm days.