Whisk together the miso, the remaining 1 tablespoon maple syrup and mustard in a small bowl and paint about half of the mixture over the top and sides of the pork. Roast, brushing again after 45 minutes with the remaining glaze, until an instant-read thermometer inserted in the center registers 130 to 135 degrees, 70 to 95 minutes. The internal temperature of the pork will rise as it browns in the next step, so if you want a faint trace of pink left, go for 130 degrees; if you prefer your pork more well done, take it to 135 to 138 degrees. But don't let it climb above 140 degrees or you will risk ruining the meat.
Turn the broiler onto high and leave the pork on the middle rack, broil until the top browns and sizzles, 2 to 5 minutes; the timing depends on the strength of the broiler. Immediately transfer the roast to a carving board, ideally one with a trough to capture any juices. Let rest for about 10 minutes; you can tent it with foil if the kitchen is cool.
Carve the pork into slices (1/4-inch-thick slices give the best combination of tenderness and meatiness). Carve only as much of the pork as you're serving, as any leftovers keep better left intact. Serve with chutney at the table.
