I've really missed soft-serve frozen yogurt.  You can never really be sure the stuff they serve at yogurt places is gluten-free, and you can be pretty sure there's cross-contamination.  I tried the obvious first:  put some store-bought yogurt into the ice cream maker.  Not only did it work, it only took a few more tweaks to make something so tasty, rich and creamy that you'll never be tempted by TCBY again.
I use the Publix store brand fruit on the bottom lowfat yogurt.  While it is fantastic straight out of the ice-cream maker, after a few hours it gets pretty hard.  I would need to thaw it out for a while (20 minutes or so) before serving once it has frozen overnight.  I could make it creamier straight from the freezer by reducing liquid and increasing fat.  That can mean using full-fat yogurt (or greek-style) or using all cream instead of cream and milk.  Added sugar will help (to a point), as will a small amount of guar gum.  Since we tend to finish it off pretty quickly, this isn't a problem.  
Homemade Frozen Yogurt 
Freeze the bucket of your ice-cream maker according to directions (usually for at least 24 hours).  Leave it in the freezer until ready to process.  
Combine the following in a separate bowl:
12 ounces of sweetened/flavored yogurt (I use fruit on the bottom)
OR
12 ounces of plain yogurt plus jam, honey, or other sweetener to taste
AND
1/4 cup whole milk
1/4 cup heavy cream
1/2 teaspoon pure vanilla extract 
1/4 cup sugar (optional, depending on flavor desired)
1 cup fresh berries or fruit, chopped small (optional) or nuts
Mix everything together
Process in ice cream freezer until slightly thicker than soft-serve
Serve immediately, or freeze up to two hours first.  After two hours, let thaw on counter for 20 minutes before serving to soften up.   
Serves 4 at 1-2 scoops each, or 2 at NOMNOMNOMNOM size servings.  
