Cook your pasta in a large pot of salted boiling water—make sure it is salty like the sea! In the last minute of cooking, add your peas and scallions. I like to thaw my frozen peas at least partially, so the water comes back to a boil as quickly as possible. Reserve some pasta cooking water (about 1/2 cup), then drain the pasta, peas, and scallions into a colander with small holes (you don't want to lose all your scallion friends!).
Return your empty pot to the stove. Warm the butter and cream over medium-low heat, until the cream starts to bubble and the butter is totally melted. Add the drained pasta, peas, and scallions, plus the grated Parmesan (be generous; be daring) and lots of black pepper. (Really. Lots!)
Stir everything together, and add a bit of pasta water to thin out the sauce. Start with 1/4 cup, then add as you see fit. Taste for salt, and add a bit more—flaky preferred—if you deem it necessary.
Divide your creamy pasta goodness into bowls, then bunch up your mint and snip it into thin ribbons with clean kitchen scissors, scattering it as a garnish. I cut it at the last minute to keep it from turning brown; you can also just use a knife if you like. You can also add chives, or tarragon, or any combination of the three—they all play well with peas and cream.