Caramelize the onions: Melt butter with olive oil in a large deep Dutch oven or heavy cast-iron skillet over medium-low heat. Add thinly sliced onions with a pinch of sea salt. Cook slowly, stirring occasionally, for 20 to 25 minutes until deeply golden brown, sweet, and jammy.

Brown the beef & aromatics: Increase heat to medium. Add the lean halal ground beef to the caramelized onions, breaking it apart with a wooden spoon. Cook for 5 to 6 minutes until browned and no pink remains. Stir in minced garlic, fresh thyme leaves, Worcestershire sauce, and Dijon mustard; sauté for 60 seconds until delightfully fragrant.

Deglaze & add pasta: Pour in 1/2 cup of the low-sodium beef bone broth to deglaze the bottom of the pan, scraping up all the golden caramelized fond with your wooden spoon. Pour in the remaining 3 cups of beef bone broth and stir in the uncooked medium pasta shells.

Simmer to al dente: Bring the skillet to a gentle boil, then reduce heat to medium-low. Cover with a lid and simmer for 10 to 12 minutes, stirring every few minutes to prevent sticking, until the pasta shells are perfectly al dente and have absorbed most of the savory beef broth.

Stir in cream & cheese: Remove the lid and reduce heat to low. Pour in the heavy cream and stir until silky. Remove the pot from direct heat and fold in 1 cup of freshly grated Gruyère cheese and 1/2 cup Parmigiano-Reggiano until completely melted and velvety smooth.

Melt bubbly cheese & serve: Scatter the remaining 1/2 cup of grated Gruyère over the top. Cover with the lid for 2 to 3 minutes off the heat (or place under the oven broiler for 2 minutes) until the cheese forms a glorious, bubbly golden blanket. Garnish with chopped fresh parsley, chives, and cracked black pepper, then serve immediately!