Bring a large pot of water to a boil. Add a large pinch of salt, then stir in the orecchiette. Cook, stirring occasionally, until al dente, 11 to 13 minutes, or according to package instructions.
Meanwhile, crumble the merguez into a large skillet, add the olive oil, then place over medium heat. Once the merguez begins to sizzle, continue cooking, stirring and breaking up the sausage into pieces as small as possible, until it has rendered its fat and is golden brown and crisp at the edges, about 6 minutes.
Add the shallots, season with salt and pepper and cook, stirring, until caramelized at the edges and soft, 3 to 4 minutes. Add the tomato paste and garlic and cook, stirring, for 1 minute. Reduce the heat to low, and stir in the fava beans and vinegar.
Drain the pasta, reserving ½ cup pasta water. Transfer the pasta to the skillet, along with ¼ cup pasta water, and toss to combine with the merguez and fava beans, adding more reserved pasta water, if needed. Remove the skillet from the heat and season with salt and pepper.
Divide the pasta among four plates. Use a vegetable peeler to thinly shave the manchego over the top of the pasta to serve.
