Step 1

DAY ONE: PREP COMPONENTS

Step 2

FOR THE BEEF: Sprinkle all sides of beef evenly with salt. Wrap in plastic wrap and refrigerate for at least 12 hours or up to 3 days.

Step 3

FOR THE PASTRY: Using stand mixer fitted with paddle, mix flour, butter, and salt on medium-low speed until mixture is crumbly and pieces of butter are no larger than peas, 4 to 5 minutes. With mixer running, add ice water in steady stream. Increase speed to medium and continue to mix until smooth dough comes together around paddle, 1 to 3 minutes longer. Transfer dough to lightly floured counter. Remove one-quarter (about 8 ounces) of dough and shape into 6-inch square. Shape remaining dough into 6-inch square. Wrap both pieces in plastic and refrigerate for at least 8 hours or up to 2 days.

Step 4

FOR THE DUXELLES: Process shallots and garlic in food processor until very finely chopped, about 30 seconds, scraping down sides of bowl as needed. Transfer to small bowl. Pulse half of mushrooms until mushrooms resemble couscous, about 10 pulses, scraping down sides of bowl halfway through processing (do not overprocess). Transfer to large bowl and repeat with remaining mushrooms.

Step 5

Melt butter in 12-inch nonstick skillet over medium-low heat. Add shallot mixture and cook, stirring frequently, until softened, 3 to 5 minutes. Stir in mushrooms, pepper, and salt and cook, stirring occasionally, until liquid given off by mushrooms has evaporated and mushrooms begin to sizzle, about 45 minutes. Add Madeira to mushroom mixture and cook, stirring constantly, until evaporated, about 2 minutes. Off heat, stir in thyme. (If making duxelles ahead, let cool completely and refrigerate in airtight container for up to 3 days.)

Step 6

DAY TWO: ASSEMBLE

Step 7

TO ASSEMBLE: Overlap 2 to 3 pieces of plastic on counter to form 30 by 30-inch square (it's OK if up to 2 inches of plastic hangs off edge of counter). Shingle prosciutto in center of plastic in 2 rows of 6 slices, slightly overlapping to form 14 by 15-inch rectangle, with shorter side parallel to edge of counter. Transfer duxelles to prosciutto and use offset spatula to spread in even layer, leaving 1-inch border of prosciutto on all sides (if duxelles is cold, microwave for 1 minute to soften before spreading).

Step 8

Unwrap beef and pat dry with paper towels. Brush all sides of beef with mustard and sprinkle with pepper. Arrange roast parallel to edge of counter, about one-third of way up duxelles. Using both hands, lift bottom edge of plastic to begin wrapping roast. Continue to roll roast, leaving plastic behind, until roast is completely wrapped in prosciutto. Tuck overhanging slices of prosciutto over each end of roast.

Step 9

Tightly roll roast in plastic and twist plastic tightly at each end to seal. Continue to twist ends of plastic and roll roast on counter until formed into snug cylinder. Refrigerate for at least 30 minutes or up to 2 days before cooking.

Step 10

Line 2 rimmed baking sheets with parchment paper. Roll out larger piece of dough on generously floured counter into 18 by 16-inch rectangle. Drape dough over rolling pin, transfer to prepared sheet, and refrigerate for 15 minutes. Roll smaller piece of dough into 16 by 7-inch rectangle. Transfer to second prepared sheet and refrigerate.

Step 11

Whisk together egg and yolk. Lay large pastry sheet directly on counter with long side parallel to edge of counter. Brush entire surface with egg wash; set aside remaining egg wash. Unwrap beef and place on pastry, arranging it parallel to edge of counter and 2 inches from pastry edge closest to you. Wrap edge of pastry closest to you over beef. Holding edge in place, slowly roll roast away from you, keeping pastry snug to meat, until roast is covered.

Step 12

Allow pastry to overlap by 1 inch and trim away excess. Roll roast so seam is on top. Gently press and pinch overlapping dough to seal. Roll roast so seam is on bottom.

Step 13

To seal ends of roast, tuck sides of pastry tightly against meat as though you are wrapping a present, then fold top of pastry down, pressing snugly.

Step 14

Using rolling pin, roll excess dough at end of roast against counter to make it thinner and longer. Trim rolled end to 2-inch length and tuck under roast. Repeat process on other end of roast. Transfer roast seam side down to lightly greased rimmed baking sheet and refrigerate for at least 15 minutes or up to overnight (if refrigerating longer than 1 hour, wrap in plastic).

Step 15

Transfer smaller rectangle of dough, still on parchment, to counter, with short side parallel to edge of counter. Using ruler and sharp knife or pizza cutter, cut dough lengthwise into ¼-inch-wide strips.

Step 16

Brush top, sides, and ends of roast with some of reserved egg wash; set aside remaining egg wash. Lay strips of dough diagonally across top of roast, leaving ¼ to ½ inch between strips. Gently press strips to adhere to roast and trim excess at each end to ¼ inch. Using bench scraper, tuck ends of strips under roast. Refrigerate roast for at least 10 minutes. (Roast can be loosely covered with plastic and refrigerated for up to 24 hours.)

Step 17

DAY THREE: BAKE AND SERVE

Step 18

Adjust oven rack to lower-middle position and heat oven to 450 degrees. Brush roast thoroughly with reserved egg wash. Place thermometer probe, if using, through 1 end of roast so tip of probe is positioned at center of roast. Roast until beef registers 85 degrees and crust is well browned and crisp, 40 to 45 minutes. Transfer sheet to wire rack, leaving probe in place to monitor temperature. Let rest, uncovered, until internal temperature reaches 130 degrees, 40 to 45 minutes.

Step 19

TO SERVE: Slide large metal spatula under roast to loosen from sheet. Use both hands to transfer roast to carving board. Using serrated knife, cut roast into 1-inch-thick slices (to keep pastry intact, score through decorative strips before cutting each slice) and serve.