No no no. First you must have a Bean Pot. This is a weirdly round yet squat casserole-type covered stoneware pot that magically distributes heat exactly right for baked beans.
The beans do not have to be Northern White. I use whatever grew best in the garden, which this year happens to be scarlet runner beans. Trout beans, pintos, any floury bean will work fine.
I don't eat pork, so my beans have tomato paste, molasses, mustard, maple syrup, brown sugar in addition to the fried onion. You pretty much put it all in to taste, with enough liquid to cover the beans well, then bake the pot kinda slowly, either in the oven or next to an open fire or in a wood-fired bread oven or some such. Sorta like a Dutch oven style hearth cooking method. But a regular oven set to 325 works too. If you use the Bean Pot, the beans get all creamy and evenly cooked. Some strange people like the crusty bits that come from uneven cooking, though.
I don't know measurements, because it depends on the size of the bean pot. Everything's just "some." Brown sugar is probably 1/2 c. but everything else gets measured in dollops.