Put a rack or two of side or back pork ribs on a rimmed baking sheet and cover with foil; bake at 300F for 2 1/2-3 hours. When cool enough to handle, separate into ribs.
In a large pot, combine:
1/2 cup maple syrup
1/4 cup soy sauce
2 Tbsp. Dijon or grainy mustard
1 Tbsp. chopped fresh rosemary
1 Tbsp. lemon juice
Add the ribs to the pot and let sit for half an hour or so, or refrigerate overnight (or for up to two days, if well covered so they don’t dry out). When ready to eat, set the pot over medium heat and bring to a simmer.
Simmer for about 20 minutes, tossing them around in the pot so that the ribs absorb some of the sauce, get glazed and and sticky, and heat through.