Kasha varnishkes turns humble buckwheat, pasta and onions into something extra special
In a large wide saucepan or skillet over medium heat, melt the remaining 1/2 cup (4 ounces) of schmaltz. Add the onions and cook, stirring occasionally, until light golden brown, 20 to 25 minutes, adjusting the heat as needed to prevent the onions from burning (see NOTES). Add the mushrooms, season lightly with the remaining salt and pepper and cook, stirring, until the mushrooms give off most of their liquid and the onions turn darker, about 10 minutes. Taste, and season with additional salt and/or pepper, if desired. Transfer the mushroom-onion mixture to the pot with the pasta.