Preheat your oven to 400°F (200°C).

In a skillet, melt 2 tablespoons of butter over medium heat. Add the sliced leeks and cook until they are soft and slightly caramelized, about 10 minutes. Remove from heat and let cool.

In a large bowl, combine the cooked leeks, thyme leaves, breadcrumbs, salt, and pepper. Mix well until the ingredients are evenly distributed.

Season the Tomahawk steak generously with salt and pepper on both sides. Heat a cast-iron skillet over medium-high heat and add a drizzle of olive oil. Once the oil is shimmering, sear the steak for about 3-4 minutes on each side until a nice crust forms.

Remove the skillet from the heat and carefully press the leek-breadcrumb mixture onto the top of the steak, ensuring it adheres well.

Transfer the steak to the preheated oven and roast for 15-20 minutes or until the internal temperature reaches your desired doneness (135°F for medium-rare).

While the steak is roasting, prepare the brown butter and Madeira-shallot infusion. In a small saucepan, melt the remaining 2 tablespoons of butter over medium-low heat. Add the chopped shallots and sauté until translucent, about 5 minutes.

Pour in the Madeira wine and allow it to simmer for 3-4 minutes until slightly reduced. Season with salt and pepper to taste.

Once the steak is done, remove it from the oven and let it rest for 10 minutes.

Slice the Tomahawk steak and serve drizzled with the brown butter and Madeira-shallot infusion.