Roast a whole head of garlic* (whatever method you choose). do the whole head and what you don't use refrigerate for another recipe.

Bring two pots of salted water to a boil and drop in the peeled and quartered sweet potatoes in one pot and the white potatoes in the second pot. Cook each pot of potatoes until they are fork tender.

While the potatoes are cooking, brown 1 stick of the butter by slowly heating it in a skillet until it is nice and brown (watch carefully as it will burn). When it is browned, add in the chopped rosemary and then turn off the heat.

Add the 1/2 stick butter and the 2 tablespoons olive oil to another skillet or saucepan and heat. Add in as much of the mashed roasted garlic as you want.  For this amount of potatoes I would add at least 6-8 cloves.

When the potatoes are done drain separately. Mash the white potatoes first with salt and pepper and some of the oil/butter/garlic mixture along with some of the warmed cream until you get the consistency of mashed potatoes. Stir in the chopped parsley.

Now, mash the sweet potatoes and add some of the browned butter with rosemary and enough milk to give you a good semi-stiff mashed potato. Salt and pepper to taste. If you are going to add the fresh ginger, add them to the sweet potatoes.

Now, the fun part. Fold the two potatoes together, gently trying not to over mix. You want to see the potato colors swirled together. Top the bowl with a large pat of butter and serve immediately or reheat in the microwave or oven.

*I cut the top off of a head (or two) of garlic, drizzled with some olive oil and then wrap in a foil bundle. Bake at 350° for 30-40 minutes. I've seen some chefs roast their garlic in an iron skillet on the stop top. I tried them in the iron skillet and got mine too brown.  I will do them from now on in the oven.