Cut the butter into tablespoon sections and dot the butter over the peas.
Sprinkle the seasonings over top.
Cover pans tightly with foil and bake at 400℉ for 20 to 30 minutes (up to 45 minutes if starting with frozen peas).
After 15 minutes, give a stir to mix in the butter and to check how they are cooking. Peas are done when steaming hot but still vibrant green. Taste for seasoning.
Notes
The 400℉ oven temperatures is provided in the recipe card, but there is flexibility depending on what else is being cooked. Peas will cook equally fine at 350℉, 375℉, or 400℉. Cook time will depend on oven temperature (hotter oven = faster cooking) and whether the peas were initially thawed or frozen (frozen peas will take longer, even up to 45 minutes).The peas are done when they are steaming hot but still green almost like when they came out of the package. Overcooking will turn the peas drab green (like canned peas).