Allow 1 or 2 pieces of marrow per person. Select marrows about 3 inches long or have your butcher cut it.
Preheat the oven at 400 degrees.
Cut a 4-inch foil and wrap the bottom of each marrow and stand in a baking pan.
Chop fresh rosemary.
Finely zest 2 lemons, preferably, Meyer lemons.
On top of each marrow, put a ½ tsp each rosemary and lemon. Sprinkle with salt and pepper.
Drizzle with olive oil.
Bake for 20 minutes.
Slice a French bagette thinly. Arrange in a baking pan and put in the oven, bottom shelf, in the last 5 minutes to crisp.
Serve with lemon wedges.
To enjoy, spoon the marrow on toast.