-
1
In a small skillet, melt the butter.
-
2
Add the coriander, all the peppercorns and the crushed red pepper and cook over moderately low heat for 1 minute.
-
3
Scrape into a medium bowl and stir in the brown sugar and 1 1/2 tablespoons of salt.
-
4
Rub the mixture all over the steak and transfer to a baking dish.
-
5
Cover with plastic wrap and refrigerate for 3 hours.
-
6
In a large saucepan of salted boiling water, blanch the leeks until just tender, 3 to 4 minutes.
-
7
Using tongs, transfer them cut side down to a paper towellined baking sheet to drain.
-
8
In a small bowl, whisk the mustard with the vinegar.
-
9
In a large cast-iron skillet, heat 1 tablespoon of the oil over high heat until smoking.
-
10
Add half of the steak and cook over high heat, turning a few times, until lightly charred on the outside and medium-rare within, 4 to 5 minutes total.
-
11
Transfer to a carving board, spread with the Dijon vinegar and let rest for 10 minutes.
-
12
Repeat with 1 tablespoon of the oil and the remaining steak and Dijon vinegar.
-
13
Wipe out the skillet and heat the remaining 1 tablespoon of oil in it.
-
14
Add the leeks cut side down and cook over high heat until lightly charred on the bottom, about 3 minutes.
-
15
Transfer to a platter and drizzle with the lemon juice.
-
16
Slice the steak against the grain and serve with the leeks.
