In a sauté pan over medium-high heat melt first amount of butter. Add sliced onions and cook, stirring often, until well browned, about 10-12 minutes. Reduce heat to medium if needed for even browning of onions
Add second amount of butter to pan along with the cremini mushrooms and cook until softened. Add garlic powder and thyme and cook until fragrant.
Add pasta, beef stock, cream, and salt. Bring to a boil then reduce heat to medium-low and simmer. Cook until pasta is cooked al dente, about 15 minutes.
Stir in half of grated cheese to cooked pasta. Portion pasta into 8 oz ramekins. Hold warm for service.
For each serving, sprinkle 1/4 cup cheese over one ramekin. Place under salamander and cook until cheese begins to brown. Sprinkle with 1/8 teaspoon chives. Serve hot.
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