Every person at the table actually moaned after their first bite of this. The first time I made this, I used very small sweet potatoes that just needed to be cut crosswise, and because I was running late I cut them into pieces closer to 1" wide. They still took longer than expected to cook, which meant that they caramelized all on their own without broiling. Glad I used a Pyrex dish! I didn't have white wine vinegar so I used equal parts rice wine vinegar and Mijiu to complement the miso. I didn't add any additional salt and the dish was utterly sublime. I've also cooked this by roasting the cubed sweet potatoes on their own until done, then pouring the sauce over them and returning them to the oven until bubbling hot.
I toast the walnuts then chop them until they're fairly small. Go heavy on the lemon zest! A medium zuke usually yields 2C grated, so I double the recipe and make 36 mini muffins. 13 - 14 minutes is plenty of time to cook these and I fully rotate the trays (I have 6 muffin trays so put 2 on a quarter sheet pan) halfway through baking. I don't sugar the tops because I think there's enough sugar already between the sugar and the raisins.