I wanted something other than a tomato-based or cream-based sauce for pasta the other day, so I stood there staring into the open refrigerator. I pulled out a baked yellow sweet potato, red miso and butter. While about 2 T butter and about 1/4 C water warmed in the micro, I mashed the sweet potato well with a fork. After dissolving about 1 T red miso in the hot butter-water, I stirred in the mashed sweet potato. (Results should be creamy; if too thick, add more water.)
The result had a distinct miso flavor from my tasting spoon, but when mixed with cooked pasta and some leftover veges, the whole thing seemed to come together nicely. I'd definitely do it again.
What unusual ingredients have you used in making non-tomato-based pasta sauce?