Mushroom Meatballs

4 Tbsp olive oil, divided

1 lb cremini mushrooms, finely chopped

1 onion, chopped

2 cloves garlic, minced

½ cup walnuts, very finely chopped (by hand or food processor)

¾ cup breadcrumbs

1 oz romano cheese, finely grated

¼ cup (packed) chopped parsley

2 eggs, beaten

½ tsp salt

¼ tsp red pepper flakes

1. Heat 2 Tbsp oil in large nonstick skillet over medium-high heat. Add mushrooms and onion. Cook until mushrooms have given off liquid and browned, and onion is soft and translucent, about 12 minutes. Off heat, add garlic and walnuts. Cool to room temperature.
2. Add breadcrumbs, cheese, parsley, eggs, salt and red pepper flakes to mushroom mixture. Mix well. Cover bowl, and refrigerate 30 minutes.
3. Preheat oven to 450 degrees. Line rimmed baking sheet with parchment paper and brush with 1 Tbsp oil. Shape mixture into balls, about 2 Tbsp each (about 22 total). Brush balls with remaining 1 Tbsp oil. Bake until golden brown, 18-20 minutes, flipping halfway through. Serve, refrigerating any leftovers.