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1
Combine the rhubarb, sugar and 3/4 cup water in a medium saucepan and bring to a boil.
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2
Reduce the heat to medium and simmer until the rhubarb is completely broken down, about 15 minutes.
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3
Strain through a fine-mesh sieve into a separate saucepan, pressing firmly on the rhubarb to squeeze out the syrup; reserve the rhubarb.
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4
Set aside 1/2 cup syrup for glazing.
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5
Make the compote: Add 1/4 cup of the rhubarb solids to the remaining syrup in the saucepan (discard the rest of the solids).
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6
Add half of the grapes, the onion, 1 tablespoon mustard, the chopped thyme, red pepper flakes and a pinch of salt.
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7
Bring to a boil, then reduce the heat to medium low and simmer, crushing the grapes with a wooden spoon, until the grapes break down and the sauce thickens, about 12 minutes.
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8
Add the remaining grapes and 1 tablespoon mustard and simmer 6 more minutes.
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9
Let cool completely.
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10
(The compote can be made up to 3 days ahead; cover and refrigerate.)
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11
Make the ham: Preheat the oven to 350 degrees F. Mix the brown sugar and the remaining 2 tablespoons mustard with the reserved 1/2 cup rhubarb syrup in a bowl; set aside.
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12
Remove the skin and all but about 1/4 inch fat from the ham.
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13
Score the fat with a small sharp knife in a tight crosshatch pattern, making the cuts about 1/2 inch apart.
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14
Put the ham flat-side down on a rack in a roasting pan.
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15
Add 1 cup water to the pan and tent the ham with foil.
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16
Roast 1 1/2 hours.
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17
Increase the oven temperature to 375 degrees F. Uncover the ham and brush with the rhubarb-mustard syrup.
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18
Continue roasting, brushing with more syrup every 15 minutes, until the ham is golden brown and glazed all over, about 1 1/2 more hours.
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19
Transfer to a platter; garnish with thyme sprigs.
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20
Serve with the grape-rhubarb compote.
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21
Photograph by Con Poulos
