Pat the 1 lb 牛柳中心切取部分，去掉银皮，根据需要捆绑成均匀圆柱形 completely dry with paper towels and season all over with ½ tsp 粗盐 and ¼ tsp 黑胡椒，现磨. Heat 1 tbsp 橄榄油 in a cast iron skillet over high heat until it just begins to smoke. Sear the 1 lb 牛柳中心切取部分，去掉银皮，根据需要捆绑成均匀圆柱形 on all sides — including the ends — for about 1 minute per side, until deeply browned all over. This should take about 4–5 minutes total. Transfer to a plate and let cool for 10 minutes.

Once the 1 lb 牛柳中心切取部分，去掉银皮，根据需要捆绑成均匀圆柱形 has cooled slightly, brush it all over with a thin, even layer of 第戎芥末. Place in the refrigerator uncovered for at least 20 minutes (or up to 1 hour) to chill and set the 1 tbsp 第戎芥末.

Pulse the cremini mushrooms in a food processor until very finely chopped (or chop by hand). Melt 1 tbsp 无盐黄油 in the same cast iron skillet over medium-high heat. Add the 1 small 葱头，切碎 and cook for 1 minute, then add the 2 cloves 大蒜，切碎 and cook 30 seconds more. Add the cremini mushrooms and 1 tsp 新鲜百里香叶, season with ½ tsp 粗盐, and cook, stirring frequently, for 10–12 minutes until all the moisture has evaporated and the mixture is dark, dry, and paste-like. Spread onto a plate and refrigerate until completely cool, about 15 minutes.

Lay a large sheet of plastic wrap on your work surface. Arrange the 6 slices 意大利熏火腿薄片，约3盎司 slices in a single, overlapping layer to form a rectangle roughly 10x8 inches — wide enough to wrap the 1 lb 牛柳中心切取部分，去掉银皮，根据需要捆绑成均匀圆柱形 and long enough to cover it end to end. Spread the cooled duxelles evenly over the 6 slices 意大利熏火腿薄片，约3盎司 in a thin, uniform layer, leaving a 1-inch border on the long edges.

Place the chilled 1 lb 牛柳中心切取部分，去掉银皮，根据需要捆绑成均匀圆柱形 along the bottom edge of the 意大利熏火腿薄片，约3盎司. Using the plastic wrap to help, tightly roll the 6 slices 意大利熏火腿薄片，约3盎司 and duxelles around the 1 lb 牛柳中心切取部分，去掉银皮，根据需要捆绑成均匀圆柱形, twisting the ends of the plastic wrap like a candy wrapper to form a tight, compact log. Refrigerate for at least 20 minutes (or up to 4 hours).

Preheat your oven to 425°F. Line a baking sheet with parchment paper. On a lightly floured surface, unfold one sheet of thawed 1 package 冷冻千层酥皮在冰箱里过夜解冻；使用一张 and roll it out slightly to about 12x10 inches. Brush the entire surface with 1 egg 鸡蛋，加1 tbsp 水打散，用于蛋液刷液 wash.

Unwrap the chilled 1 lb 牛柳中心切取部分，去掉银皮，根据需要捆绑成均匀圆柱形 log and place it in the center of the 冷冻千层酥皮在冰箱里过夜解冻；使用一张. Roll the 1 package 冷冻千层酥皮在冰箱里过夜解冻；使用一张 tightly around the 1 lb 牛柳中心切取部分，去掉银皮，根据需要捆绑成均匀圆柱形, pressing to seal the seam firmly. Tuck the ends under like a gift wrap and press to seal. Place seam-side down on the prepared baking sheet. Brush the entire surface generously with 1 egg 鸡蛋，加1 tbsp 水打散，用于蛋液刷液 wash. Use a sharp knife to lightly score a crosshatch or diagonal pattern on top (do not cut through). Sprinkle with ¼ tsp 粗海盐用于最后撒用 if using. Refrigerate for 10 minutes before baking.

Bake at 425°F for 22–28 minutes, until the 1 package 冷冻千层酥皮在冰箱里过夜解冻；使用一张 is deep golden brown and an instant-read thermometer inserted into the center of the 牛柳中心切取部分，去掉银皮，根据需要捆绑成均匀圆柱形 reads 125°F for medium-rare (the temperature will rise 5°F as it rests). For medium, pull at 130–132°F. Do not open the oven door during the first 20 minutes.

Transfer the Wellington to a cutting board and let it rest, uncovered, for 8–10 minutes. Use a sharp bread knife to slice into two thick portions and serve immediately.