Sort the dried field peas, removing any broken beans, stones, and dirt clods. Rinse the peas in a fine mesh strainer.

Melt the butter in an Instant Pot set to Sauté mode adjusted to high (or a stovetop pressure cooker pot over medium-high heat). Add the smoked sausage, onion, and garlic, and sprinkle with ½ teaspoon salt and ½ teaspoon red pepper flakes. Sauté, stirring often, until the onions soften and start to brown around the edges, about 8 minutes.

Pour the sorted and rinsed field peas into the pressure cooker, pour in the 5 cups of water, and stir in 1½ teaspoons of salt. Lock the lid on the pressure cooker and cook at high pressure for 12 minutes in an Instant Pot or other electric PC (Use Manual or Pressure Cook mode in an Instant Pot, set for 12 minutes) or for 10 minutes in a stovetop PC. Quick release the pressure. Remove the lid carefully, opening it away from you – even when it's not under pressure, the steam in the cooker is hot.

Add the green beans to the pressure cooker pot. Lock the lid on the pressure cooker and cook at high pressure for 1 minute (Use Manual or Pressure Cook mode in an Instant Pot, set for 1 minute). Quick release the pressure. Remove the lid carefully (again).

Stir ½ teaspoon of fresh ground black pepper into the pot of field peas and snaps, serve, and enjoy!