To make the sauce: Heat a saucepan over medium heat. Add the unsalted butter and sprig of thyme. Melt until it turns brown, about 5 minutes. The second the butter starts becoming a medium brown, take the pan off the heat. Add the white truffle oil and mix. Reserve 2 tablespoons of this butter sauce to pan fry the ravioli.
To the saucepan add: the heavy cream, and sea salt and coarsely cracked pepper, to taste. Whisk until the mixture is emulsified.
To make the ravioli: Heat the extra-virgin olive oil in a pan over medium heat. Add the garlic and hot chile flakes to the pan and saute until the garlic becomes golden, about 2 minutes. Throw in the portabella mushrooms, minced shallots, sea salt, and freshly ground pepper, and saute for 8 minutes. Add the Swiss chard to the pan along with a touch more sea salt and freshly ground black pepper. Saute a few minutes until the chard has wilted. Take the pan off the heat and let it cool.
In a big bowl, mix the softened mascarpone cheese, ricotta cheese, 1/4-cup grated Parmesan cheese, sea salt, and freshly ground black pepper. Add the sauteed Swiss chard mixture. Delicately mix together.
Using a ravioli cutter, cut the pasta into 2-inch shapes: circles, or squares. Lightly wet the edges of the pasta with water using your finger. Place 1/2 teaspoon of the Swiss chard-cheese filling in the center of the pasta. Wet the edges of another piece of pasta, and place it on top. Use a fork, or your fingers to seal the pasta together. Make sure you seal it tight. Repeat until no filling remains.
Boil the ravioli in salted water for 6 minutes. Strain.
Pour the 2 tablespoons of brown butter sauce into a frying pan. Add a teaspoon of olive oil and turn up the heat to medium-high. Place the ravioli into the pan and sear them for a minute on each side, until golden bits appear.
Line the ravioli up on a plate, drizzle them with 2 to 3 tablespoons of sauce and sprinkle with Parmesan shavings.