This is a re-purposed spicy red miso sauce with pork (niku-miso with red miso and pork 肉味噌) I made a few days ago. Since I made it a bit too spicy (I am not sure if it was due to the Sriracha sauce or the jalapeno pepper), but it was a bit much for my wife. So we added yogurt like we often do for Indian curry which made it much milder. That led me to come up with this dish as a final "shime" 締め one evening. I made the sauce for the udon noodles from the spicy red miso sauce with pork and yogurt.
Although adding yogurt may be somewhat unusual for more traditional Japanese recipe of "Niki-miso udon 肉味噌うどん", it went well. I also added spinach which my wife prepared from fresh spinach for spinach soufflé (which we did not make because we ran out of time and energy and were too full to eat it anyway).
For a impromptu dish made from re-purposed ingredients, as leftover control, this was quite good.
I warmed up my spicy pork red-miso sauce, added yogurt (did not measure, plain non flavored) and mixed. When it was warmed up, I mixed in the cooked spinach.
We used dried thin udon noodles, Sanuki undon 讃岐うどん, cooked as per the package directions and rinsed in cold running water after it was cooked and drained.
The addition of yogurt made the sauce mild and creamy without adding much additional taste but a nice smooth texture. It easily clung to the noodles and was a perfect small ending dish for us.