No dissolved CO2 = no foam. Even the soapiest, lipid/protean saturated liquids don't foam if there are no included/dissolved gasses. So one thing to try is to reduce the amount of sugar added.
Dissolving the brown sugar in cold water is not unreasonable but dissolving it in (less volume of) boiled water and then diluting down will pasteurise the sugar to ...
Butter Buds may be a good option for you. (http://www.butterbuds.com/home.html)
It has a very buttery flavor. It is fat free which means it won't kill your head retention.
While I haven't brewed with it, I have brewed with fat free peanut butter powder for my peanut butter chocolate stout and it worked very well. You should be able to find Butter Buds ...
1⁄4 ounce dried sassafras root, bark (optional)
1⁄4 ounce dried birch bark
1⁄4 ounce dried sarsaparilla root
1⁄8 ounce dried licorice root
1.5 inch piece gingerroot, grated
1 split vanilla bean
4 quarts water
1 cups molasses
1 cup honey
1⁄8 teaspoon active dry yeast.
(optional: 1/2 a jalapeno chili pepper, for some extra anti oxidants, and make the flavors ...
I'm not sure how you like your root beer, but to get a taste similar to commercial root beers, you'll need a completely different recipe.
Here is a related question:
How would I make Alcoholic Rootbeer?
I just finished making a 5gal batch of natural root beer using danelion root, burdock root and sassafras, along a small amount of wheatgrass and beet juice (for colour).
I used a combination of white sugar, honey and mollasses to ferment and a combination of lactose and stevia to sweeten. I reused an English Ale yeast from an IPA I made a while ago and ...
18# gw base malt, 2# choc., 4oz black or roast barley, 1# oats or flaked barley. Used 2nd runnings for root beer stout. to boil add 1 pt. molasses + 1 c. pale dry extract + 2oz root beer extract. lightly hop with 2 oz cascade. ferment as usual. og 1.065 fg 1.013 . kegged & force carbonated. sweeter than typ. ales, dryer than sodas. many ...