2 large or 3 medium ears corn, shucked
3 tbsp. butter
2 leeks, white and pale-green parts only, halved lengthwise and thinly sliced
About 1/3 cup gochujang (Korean hot pepper paste)
6 cloves garlic, chopped
1-inch piece of fresh ginger, peeled and grated or finely chopped
1 bunch lacinato kale or Swiss chard, center stems removed and leaves cut into ribbons
About 1/4 cup soy sauce or liquid amino
2 tbsp. (packed) light brown sugar
2 tbsp. rice vinegar
4 tsp. toasted sesame oil
12 oz. soba (buckwheat noodles)
1 English cucumber or 4 small Persian cucumbers, chopped, plus thin slices for serving
3 tbsp. toasted sesame seeds
Gochugaru (Korean-style red pepper), optional, for passing at the table
Bring a large pot of water to a boil for the soba.
Invert a small bowl inside a large bowl. Working with 1 ear of corn at a time, steady the larger end on top of the small bowl. Using a sharp knife, cut the kernels off the cobs into the large bowl.
Heat a large deep skillet over medium-high. Add the butter. When it melts, add the corn and leeks. Cook, stirring often, until browned in spots, about 5 minutes. Add the gochujang, garlic, and ginger. Cook, stirring often, until aromatic, about 1 minute. Add the kale. Cover and reduce heat to medium-low. Cook, tossing often, until the kale is wilted, about 5 minutes.
In a large bowl, whisk the soy sauce, sugar, vinegar, and oil with about 1/3 cup of the boiling water for the soba. (This will melt the sugar into the sauce.)
Add the soba to the boiling water. Cook until al dente, about 5 minutes. Drain, then run under cold water to cool. Drain well.
Toss the corn and kale, the cold soba, the chopped cucumber, and the sesame seeds with the sauce. Top with sliced cucumber. Pass gochugaru at the table, if desired.