How to Make It
In a medium saucepan, melt the butter. Add the onion and garlic and cook over moderate heat, stirring occasionally, until softened, about 8 minutes. Add the cinnamon stick and star anise and cook, stirring, until fragrant, about 1 minute. Stir in the fish sauce and sugar and cook for 1 minute. Add the stock and simmer over moderately high heat until reduced to 1 cup, about 15 minutes. Add the cream and simmer until the sauce is thickened and reduced by half, about 10 minutes longer. Strain the sauce through a fine-mesh sieve set over a medium bowl; discard the solids. Return the sauce to the saucepan and stir in the crushed peppercorns. Season with salt and keep warm.
Heat a large cast-iron skillet. In a large bowl, toss the broccoli, cauliflower and Romanesco with 1 tablespoon of the oil. Working in batches, cook over moderately high heat, turning occasionally, until lightly charred all over and crisp- tender, about 15 minutes. Transfer to a work surface and let cool. Cut into bite-size pieces and wipe out the bowl. In the bowl, whisk the mayonnaise with the mustard, vinegar and hot sauce until smooth. Fold in the charred vegetables, the red onion and sunflower seeds and season the salad with salt. Wipe out the skillet.
In the skillet, heat the remaining 2 tablespoons of oil. Season the steaks with salt and pepper and cook over moderate heat, turning once, until an instant-read thermometer inserted in the thickest part registers 125° for medium-rare, 6 minutes per side. Transfer to a work surface and let rest for 5 minutes. Serve with the peppercorn sauce and the charred-vegetable salad.