Adjust oven rack to middle position and heat oven to 375 degrees. Heat oil in ovensafe Dutch oven or pyrex dish over medium heat until shimmering. Add onions and cook, stirring occasionally, until well browned, 12 to 14 minutes.
Add water and broth, cover, and bring to boil. Off heat, stir in rice and salt. Cover, transfer pot to oven, and bake rice until tender, 65 to 70 minutes.
Remove pot from oven and uncover. Fluff rice with fork, quickly scatter the peas on top, and replace lid; let stand 5 minutes. Uncover and let cool completely, tossing once or twice. Discard the bay leaves.
Freeze it: Divid into 1-cup portions and transfer to resealable plastic sandwich bags Squeeze out the air and flatten the bags. Seal and store flat in 2-gallon freezer bags.
Use it: Thaw at room temperature for abotu 30 minutes, or pop into the fridge in the morning and thaw all day. (The microwave can be used in a pinch.)
Change it: Half the amount of onions and add 3 minced jalapenos. Use corn instead of peas and add chopped cilantro. Swap in 1 cup white wine for 1 cup broth. Add thyme or rosemary when cooking the onions. Omit the peas and stir in chopped olives and toasted almonds.