1 3/4 lbs peeled sweet potatoes, cut in large chunks

2 tsp. butter or coconut oil, plus more for cooking

1 leek, halved and thinly sliced

2 tsp. tamari or soy sauce

1 clove garlic, minced

3/4 tsp. salt

pinch of red pepper flakes

1/2 cup oat flour or unbleached all purpose flour

1 egg, well whisked

yogurt sauce

1/2 cup greek yogurt

2 Tbsp. lemon juice

1 Tbsp. extra virgin olive oil

3 Tbsp. chopped cilantro or basil

2 Tbsp. finely chopped lemongrass*

pinch of salt and pepper