- Salt your steak generously on all sides and place on a rack in the fridge, uncovered, for at least half a day and up to 3 days. Remove at least an hour before cooking to bring up to room temperature.
- To start the chimichurri, grill all of your jalapeños directly over an open flame until fully blackened and charred all over. Transfer to an airtight container to steam and cool.
- Meanwhile, make your mac 'n' cheese. Melt the butter in a pan and add the flour. Cook for a minute or so, until it smells biscuity, then beat in the milk in stages until fully incorporated. Bring to a simmer to bloom the flour and reach the desired consistency. Season with nutmeg, mustard, salt and pepper, then stir in the creme fraiche. Add the provolone cheese in two stages, stirring constantly to melt through.
- Cook your pasta in salted water several minutes shy of al dente. Drain well. Preheat the oven to 200°C / 400°F.
- Butter a baking dish and add your pasta. Pour over the majority of the cheese sauce and stir to combine in the dish, leaving enough sauce to cover the top of the dish. Add the cheddar cheese to the remaining sauce, beat well then pour over the top of your Mac n cheese. Set aside to sit uncovered for 15 minutes.
- Meanwhile, remove the skin from your charred chillies. Deseed the majority (this is up to you, if you like it hot, leave the seeds in). Finely chop the flesh and add to a bowl. Finely chop all of the herbs, preferably in batches, then add to the chopped jalapeños. Add the shallots, garlic, red wine vinegar and loosen with olive oil. Season to taste with salt. Cover and set aside.
- Bake the mac 'n' cheese in the oven for 30 minutes, or until bubbly and the top is burnished and golden.
- Add a layer of neutral oil to a heated cast iron pan, and, when starting to smoke, carefully lay in your steak. Cook for about 4 minutes on each side, turning occasionally, or until the internal temperature reaches 52°C / 125°F. Before your steak reaches this internal temperature, add the garlic and butter to the pan and baste your steak liberally, preferably for about 5 minutes to ensure the best flavour. Remove to rest for 10 minutes. Lower the heat and tear your bread into the brown butter and fry, turning frequently, until crunchy and golden.
- Slice the steak against the grain and arrange on a plate with the mac 'n' cheese and the crunchy croutons. Cover the lot in the chimichurri sauce. Dig in.