Melt the butter and olive oil in a large pot over medium heat. Add the diced onions with a pinch of salt and stir to combine. Cover and cook for 5-10 minutes, until the onions have softened.

Remove the lid and reduce the heat to medium-low. Continue cooking the onions for 25-30 minutes, stirring every few minutes, until deeply caramelized and a rich golden brown. If the bottom of the pot starts to get too dark, reduce the heat slightly.

Meanwhile, preheat the oven to 375°F and line a baking sheet with parchment paper. Spoon the grated Gruyère onto the baking sheet in small piles, using a heaping tablespoon for each. Leave a little space between each pile and top with freshly cracked black pepper.

Bake the Gruyère crisps for 10-13 minutes, until melted and lightly golden around the edges. Remove from the oven and let cool completely on the baking sheet. They’ll crisp up as they cool.

Once the onions are deeply caramelized, add the balsamic vinegar. Cook for 1-2 minutes, stirring and scraping up any browned bits from the bottom of the pot, until the vinegar has mostly evaporated.

Pour in the beef stock, then add the thyme sprig and ditalini. Increase the heat to medium-high and bring to a bubble, then reduce to medium-low. Cook according to the ditalini package directions, stirring occasionally so the pasta doesn’t stick to the bottom of the pot, until the ditalini is tender, about 10-14 minutes.

Remove and discard the thyme sprig. Pour in the heavy cream and stir until everything is creamy and combined. Taste and adjust the seasoning with salt and black pepper as needed.

Ladle into bowls and serve with fresh chives and the Gruyère crisps.