Pan-Seared Rump Steak with Brioche-Crusted Potato and Leek Gratin

Preheat the oven to 190°C (375°F) and position the cooking rack in the center position.

Peel the russet potatoes and slice them uniformly into 3 mm rounds using a mandoline slicer, keeping them unrinsed to retain natural starch for thickening.

Trim the dark fibrous tops and roots from the leeks, slice the tender pale parts into 5 mm rounds, and rinse thoroughly in cold water to wash away residual grit.

Melt 15g of unsalted butter in a large nonstick skillet over medium-low heat at 130°C (266°F), add the washed leeks with 1g of fine sea salt, and sauté for 8 minutes until translucent and tender without taking on brown color.

Combine the heavy cream, whole milk, 3 smashed garlic cloves, 4 thyme sprigs, ground nutmeg, 3g of fine sea salt, and 1g of black pepper in a medium saucepan, bringing to a gentle simmer at 85°C (185°F) for 5 minutes, then discard the garlic and thyme sprigs.

Toss the coarse brioche crumbs, 20g of melted unsalted butter, and 1g of fine sea salt in a small bowl until the crumbs are uniformly saturated.

Coat the interior of a 2-liter baking dish with 15g of softened unsalted butter, then arrange one-third of the sliced potatoes across the bottom, top with half of the cooked leeks and 50g of grated Gruyere cheese, repeat with another layer, finish with the remaining potatoes, and pour the warm infused cream mixture evenly over the top.

Cover the baking dish tightly with aluminum foil and bake in the oven at 190°C (375°F) for 40 minutes until the potatoes are tender when pierced with a knife.

Remove the aluminum foil, sprinkle the remaining 50g of grated Gruyere cheese and the prepared brioche crumbs across the surface, and bake uncovered at 190°C (375°F) for 15 minutes until bubbly and crisp.

Pat the beef rump steaks thoroughly dry on all sides using paper towels to ensure effective searing, then season evenly with 6g of fine sea salt and 2g of black pepper, washing hands and using dedicated raw meat boards to eliminate cross-contamination.

Heat 30ml of olive oil in a heavy cast-iron skillet over high heat at 210°C (410°F) until the oil shimmers and produces faint wisps of smoke.

Carefully lay the seasoned rump steaks into the hot skillet using kitchen tongs and sear undisturbed for 3 minutes to develop a deep mahogany crust.

Turn the steaks with tongs, immediately add 40g of chilled unsalted butter, 3 unpeeled crushed garlic cloves, and 4 thyme sprigs to the skillet, tilt the pan slightly, and baste continuously using a large spoon for 3 to 4 minutes until an instant-read digital food thermometer placed in the thickest section reaches 63°C (145°F).

Transfer the seared rump steaks to a warm cutting board and rest undisturbed for at least 3 minutes, allowing internal muscle juices to redistribute and temperature to stabilize.

Slice the rested rump steaks across the grain into 8 mm thick slices with a chef's knife, portion onto warmed plates, and serve alongside generous slabs of the crisp brioche-topped potato and leek gratin.