Double Duchess Potatoes

Several people have suggested that I post some of Mimi's recipes on our blog, so here's the first one--just in time for Thanksgiving. When Mimi and I both heard of mashed potatoes (specially seasoned) and sweet potatoes (specially seasoned) on the same plate, neither of us thought it a very good idea! But we both changed our minds as soon as we ate them. They are delicious! "Try it! try it and you may, I say!" This goes so-o-o well with turkey and dressing. I have my own herb garden so the sage is readily available and the chives were in our Washington home and I'll plant some here next spring. The notes in the recipe are Mimi's words.
May you have a blessed Thanksgiving. Papaw

Double Duchess Potatoes
[Note: I use fresh herbs so increase the amount. Adjust by taste.
2nd note: you can prepare this dish the day before and then heat at 350o covered with aluminum foil for 30 minutes.]

2 lbs. Baking potatoes, peeled, cut into 1" pieces
2 1/4 lbs. Sweet potatoes, peeled, cut into 1" pieces
2 cloves garlic, peeled
2/3 cup buttermilk, warmed
½ cup butter or margarine, divided
1/4 teaspoon dried thyme
1 teaspoon salt, divided
1 teaspoon pepper, divided
1/4 teaspoon dried sage
optional: 2 Tablespoons chopped chives for mashed potatoes

Preheat oven to 375o
In separate pots combine potatoes with enough water to cover.
Add garlic to baking potatoes.
Over high heat bring both pots of potatoes to boil; reduce heat to medium.
Cook until tender; drain separately.
Return to pots. Mash baking potatoes and garlic with buttermilk, 1/4 cup butter, thyme, ½ teaspoon salt and ½ teaspoon pepper and optional chives until smooth.
Mash sweet potatoes with sage and remaining butter, salt and pepper.
Intersperse mounds of sweet and baking potatoes in ungreased casserole.
Bake until hot, 15 minutes.