To a pan over medium heat, add the olive oil and butter. Once they are heated, add the onions and salt and sauté until slightly translucent. Add the garlic and cook until it is fragrant and slightly browning. Do not burn the garlic.
Once the onions are full translucent and the garlic is cooked- add the stock, wine, parsley, lemon juice, and red pepper flakes.
Simmer over medium high heat until the liquid is cooked down by half. Taste test here, and add more salt if you'd like. The scallops and shrimp will be cooking in this so it is important to salt here.
While the liquid is simmering, bring a pot of water almost to a boil to prepare for cooking your pasta. Add the pasta to this pot when you add the shrimp and scallops to the other pan.
Once the liquid is cooked down, add the shrimp and scallops to the pan. Arrange them so that they are in a single layer. Cook until they are no longer translucent.
Turn the heat in the pan to medium low and add the pasta straight from the boiling water. The pasta should be al dente- undercooked by about one minute. The pasta will absorb the liquid in the pan and take on all that delicious flavor.
Once the pasta is completely cooked, remove the pan from heat & serve! I like to top this with some Pecorino Romano, it adds a nice sharp flavor & coats the seafood perfectly.