Preheat the oven to 375°F. Add the cherry tomatoes, oregano, and garlic to a large 10” cast-iron skillet. Cover with the olive oil, and season with the salt & lots of freshly cracked black pepper. Toss to combine. Roast for 1 hour until the tomatoes are soft and caramelized.
Meanwhile, add the cubed baguette to a food processor. Pulse until finely chopped. Heat a skillet over medium heat and add enough olive oil to cover the bottom. Once hot, add the breadcrumbs. Toast for a couple of minutes until golden and crisp, stirring often. Transfer the breadcrumbs to a large bowl and toss them with a good pinch of salt plus the chopped fresh herbs. Let cool.
Bring a large pot of salted water to a boil. When the tomatoes have about 5 minutes of roasting left, drop the fettuccine. Stir well and cook for 1 minute less than the package’s instructions.
Remove the roasted tomatoes from the oven and let cool for a minute or so. Discard the oregano sprigs. Transfer the entire mixture to a blender. Blend until smooth. Slowly add in the mascarpone, parmesan, and 1 cup of starchy pasta water from the pasta pot, blending until incorporated.
Drain the pasta and add it back to the pot. Pour in the creamy tomato sauce and stir really well to combine. Over low heat, continue to stir for a minute or so until the sauce clings to the pasta. Taste the pasta and season with more salt if needed.
Serve the pasta with the herb breadcrumbs and fresh basil over top.