It wasn't obvious (to Watanuki at least) he couldn't see how Yuuko seemed to know immediately, the reason why Doumeki seemed to like his food so much. But now that he knows, it still doesn't make sense to him. True, the expressionless food that his charge had made was kind of lifeless, but why did Doumeki like his food so much? Sometimes he pondered while he was cooking.
Now Watanuki pays more attention to the fact that he has a tendency to put in a little extra wine when he marinates the meat (much to Yuuko's delight of course), like his father had. He puts a little extra sugar into the mousse because he uses bitter chocolate, he puts a little less water than conventional when he cooks rice because it needs to be stored in a bento box and sometimes the steam rises and makes the rice sticky.
He may have forgotten his parents but he knows that his father taught him to cook, and his body remembers this and perhaps his body remembers his parents as well. So Watanuki will keep cooking, not with the solemnity of honoring memories forgotten but for the joyful memories to come and because he knows that, somewhere, he still remembers. Cooking is the way he can meet his parents.
Watanuki's food is obviously delicious. There's a quality to it that didn't have anything to do with skill, innovation, inspiration or training, though Watanuki of course has those. If Doumeki were to put a name to it he would have to say it were emotion. Watanuki loves cooking, he loves giving, he loves that people love his food, even if he's too blind to realize that maybe its him that they love.
And he knows that Watanuki's love isn't for him, at least not as of now, but Doumeki is alright with being second to Watanuki's parents because, in reality, that's who he cooks for, before his friends, before Yuuko, before even himself. He cooks for his parents. And, after all, if it had been Doumeki who'd been forgotten then he would want to be remembered, even if it were just bodily. But he hasn't been, so he'll allow it because he knows that Watanuki's parents would have wanted him to be happy. Because Doumeki is a patient person.
But even Doumeki can't wait forever and some day Watauki is going to have to admit it.
