Clean the clams
Scrub clams under cold water to remove any debris and set aside. Discard any clams with broken shells.
Cook the pasta
Bring a large pot of salted water to a boil. Add the pasta and cook, until al dente, about 10 minutes. Reserve 1 cup of the pasta cooking water. Drain and return the pasta to the pot.
Cook the pancetta
Heat a large heavy bottomed pot over medium heat, add the olive oil and heat. Add pancetta and cook until crispy and the fat has rendered. Use a slotted spoon to remove the pancetta and set aside.
Add the shallots and garlic and cook, stirring occasionally, until the shallots are tender and translucent, about 5 minutes.
Stir in the red pepper followed by the wine and bring to a simmer.
Steam the clams
Arrange the clams in the pot and increase the heat to high. Cover and steam until the clams open, about 6 to 8 minutes, depending on the size of the clams.
After the clams open, use tongs to transfer them to a bowl, discarding any clams that did not open. Remove half the clams from the shells and roughly chop, leaving some in the shells as garnish.
Stir the butter into the sauce, continuing to stir until the butter has melted. Add the crispy pancetta back to the pot along with the chopped clams and half the parsley.
Reduce the heat to medium and add the pasta to the pot, tossing in the sauce and covering until the pasta is warm and has absorbed some of the sauce, adding ½ cup of the pasta water.
Use tongs to transfer the pasta to warm pasta bowls. Top with the reserved clams in the shells and divide the remaining sauce among the bowls; garnish with parsley.