In a Dutch oven or heavy-bottomed pan, heat 3.5 tablespoons olive oil and 3.5 tablespoons unsalted butter over medium heat. Add the 1.5 cups finely diced yellow onion, stir, cover, and cook for 5-10 minutes until translucent.
Stir in the 1 cup finely diced celery and 1 cup finely diced carrot. Cover and cook for another 5-10 minutes until softened and slightly browned. Add 3 crushed garlic cloves and cook for 1 minute.
Add 16 ounces ground pork, breaking it up with a wooden spoon. Increase to medium-high heat and cook for 8-10 minutes, until the pork is browned and no longer pink.
Pour in 1 cup dry white wine, stirring to combine and scraping up any browned bits from the bottom of the pan.
Add 1 cup whole milk and bring to a simmer. Add 1/2 teaspoon ground black pepper, 1 teaspoon salt, 1/4 teaspoon ground nutmeg, and 1/2 teaspoon ground sage.
Add the Parmesan rind and the sprig of thyme.
Reduce the heat to low, cover, and simmer for about 1 ½ hours, stirring occasionally. If the sauce thickens too much, add a little pasta water as needed to adjust the consistency.
Once the sauce has thickened and developed rich flavor, remove the parmesan rind and thyme sprig. Stir in 2 tablespoons mascarpone cheese and 1/4 cup heavy cream. Adjust seasoning to taste.
In a large pot of salted water, cook 1 pound pappardelle pasta until al dente according to package instructions. Drain and toss with the white bolognese sauce.
Top with freshly grated Parmigiano Reggiano and torn fresh basil. Enjoy!