Place a saucepan on medium heat and add the olive oil.
Stir in the diced steak, pork, and chicken thighs. Brown all the meat for 5 minutes.
Pour the white wine and water into the saucepan and bring it to a simmer.
Place a lid on the pot and cook the meat for 40 minutes until tender.
Next, remove the meat from the saucepan and finely chop it (or grind using a meat grinder), keep the cooking liquid in the saucepan to prepare the sage sauce.
Place a saute pan on medium heat then add the spinach and garlic, letting it cook for one minute until wilted.
Discard the garlic and stir the spinach into the meat mixture along with the egg and parmesan cheese.
Divide the pasta dough into four equal pieces then pass each through a pasta machine, working from the widest setting to the second to last setting.
Lay the pasta sheets onto a work surface and trim them to form 3-inch wide rectangles.
Place one teaspoon of the meat mixture on the pasta dough, then continue adding more of the filling, leaving an ½-inch gap between each one.
Fold the pasta sheet over to seal the filling in, then pinch between the gaps to remove any air pockets.
Slice individual agnolotti using a pasta wheel to cut between each filling then dust them with semolina flour.
Prepare the sauce by using the saucepan with the meat cooking liquid, then add the chicken broth, butter, and sage.
Place the saucepan on medium heat and simmer for 5 minutes to melt the butter and form a thickened sauce.
Bring a large pot of water to a boil.
Once boiling, season the water with salt and add the agnolotti dal plin.
Cook the agnolotti for two minutes, then transfer them directly to the sage sauce and warm through.
Serve the traditional agnolotti dal plin immediately with grated parmesan cheese.