In a large skillet, heat 2 tablespoons of olive oil over medium-high heat. Add 2 sliced yellow onions and sauté for 10 minutes until softened. Reduce heat, sprinkle with ¼ teaspoon salt, and cook for another 20 minutes until deep golden brown. Set aside.

In the same skillet, add 1 tablespoon of olive oil and the sliced crimini mushrooms. Lightly season with salt and sauté for about 5 minutes until softened. Stir in fresh spinach, cooking until wilted, about 2 minutes.

Return caramelized onions to the skillet with mushrooms and spinach. Pour in 1 cup of heavy cream and add ¼ teaspoon salt. Bring to a gentle boil, stirring constantly, then reduce heat and simmer for about 5 minutes to thicken.

Meanwhile, cook 9 ounces of refrigerated tortellini according to package instructions, usually 7-10 minutes. Drain tortellini and add directly to the creamy sauce, stirring gently to coat.

Allow tortellini to heat through in the sauce for about 2 minutes, tossing gently. Serve immediately, topped with cracked black pepper to taste.