Using your paella pan, heat 2 tablespoons of olive oil over medium-high heat. Add in the onions and sauté until softened, for about 3 to 4 minutes. Stir in the garlic and continue to sauté until fragrant, for about 1 to 2 minutes.
Add in the tomato sauce, season with salt and pepper and add in the smoked paprika and the saffron threads, mixing well, and cook for about 4 to 5 minutes. Add in the rice and stir well until all the grains are coated with the tomato sauce mixture and the rice is evenly distributed around the skillet or pan.
Using a separate small saucepan, bring the chicken stock and wine to a boil and then pour evenly over the rice. Turn up the heat to high and bring to a boil, and season with salt.
Turn the heat down to low and let the rice simmer for about 15 to 20 minutes. If it looks like you need more liquid to help your rice cook, you can add just a little more tomato sauce (1/4 cup to a 1/2 cup depending on how much you need) and more chicken stock to the rice, halfway through cooking. If you do this, pour evenly over the rice and then make sure the rice is still evenly distributed over the skillet.
Add in the sausage, either chopped or broken up into pieces and evenly distribute all over the rice and stir and cook until the sausage is cooked and browned completely. As your paella is cooking, remember to keep mixing around the pan so it doesn't stick to the bottom as much. A little sticking is ok but you just don't want it to burn.
While the rice is cooking, prepare the mussels.
For the mussels:
Using a large sized saucepan or small pot, warm the butter and olive oil over medium-high heat, waiting until the butter has melted. Add in the minced shallots and garlic and sauté until the shallots are translucent and the garlic is fragrant, for about 1 to 2 minutes.
Add the mussels into the saucepan and pour in the chicken stock and wine or water. Immediately cover the pan with the lid for about 5 minutes. After about 5 to 6 minutes, lift the lid and check the mussels. Nearly all of the mussels should be open by now. If not, cover and cook an additional 1 to 2 minutes. You can mix the mussels around in the saucepan to get the sauce nicely distributed over them. Discard any mussels that haven’t opened after this time. Do not consume any mussels that have not opened.
Once the rice is cooked, arrange the shrimp and tomatoes evenly over the rice and let cook. After the shrimp start to turn pink, flip them over and cook the other side. You want to cook the shrimp until they are just pink. Do not overcook.
Arrange the open mussels on top of the seafood paella, drizzle the remaining tablespoon of extra virgin olive oil over the top of the paella, garnish the parsley and serve immediately. Enjoy!