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1
Preheat oven to 425F.
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2
Pat beef dry and cut 1/2-inch-deep slits at 1-inch intervals all over roast, then insert 1 piece of pancetta into each slit.
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3
Sprinkle beef with kosher salt and pepper.
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4
Heat oil in a 12-inch heavy skillet over high heat until just smoking, then brown beef on all sides, about 5 minutes.
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5
Transfer beef to a small roasting pan, reserving skillet.
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6
Roast beef in middle of oven until an instant-read thermometer inserted diagonally 2 inches into center registers 120F, about 25 minutes.
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7
Transfer beef to a cutting board and let stand, loosely covered with foil, 25 minutes.
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8
(Beef will continue to cook as it stands, reaching 130F for medium-rare.)
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9
Heat reserved skillet over moderately high heat until oil is hot but not smoking, then saut e shallot until golden, about 2 minutes.
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10
Add red wine and Marsala and deglaze skillet by boiling, stirring and scraping up brown bits, until liquid is reduced by about one third.
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11
Add demiglace and jelly and briskly simmer, whisking, until jelly is incorporated, about 2 minutes.
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12
Add butter, 1 bit at a time, whisking until incorporated, then remove from heat.
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13
Whisk in salt and pepper.
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14
Pour sauce through a fine sieve into a bowl, pressing on solids.
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15
We use Demi-Glace Gold, available in specialty foods shops, some supermarkets, and by mail order from More Than Gourmet (800-860-9385) or the demiglace/brown sauce from Citarella (212-874-0383).
