INGREDIENTS
1.4 cup olive oil, plus more for drizzling and to toast bread
2 tsp freshly ground black pepper, plus more to garnish
2 tbsp kosher salt
3 tbsp minced thyme leaves
5 lbs top sirloin roast, trimmed and tied
1 batch horseradish cream
1 sliced of grilled sourdough bread per person
crunchy sea salt to finish
For the Horseradish Cream
1 cup sour cream
1/2 tsp dijon mustard
1/4 cup freshly grated horseradish root
1/2 tsp lemon juice
kosher salt and freshly ground black pepper
DIRECTIONS
In a medium bowl, which together the olive oil, black pepper, salt, and thyme. Run all over the sirloin, cover well, and refrigerate overnight.
Heat the oven to 325. Pull the roast from the refrigerator, place it on a sturdy baking sheet, and let it sit at room temperature for one hour. Roast the beef for 75 to 90 minutes, or until a thermometer inserted into the deepest part of the roast reads around 120 for a rosy, rare interior. Remove the meat from the oven and cover with aluminum foil; the temperature will continue to rise for about 20 minutes. Let it cool entirely., placing it in the refrigerator once at room temperature, if you are finishing the tartines the next day.
When you are ready to serve, remove the strings on the roast and slice as thinly as possible, aiming for paper-thin ruffles.
To make the horseradish cream, in a medium bowl, combine the sour cream, mustard, horseradish, lemon juice, and salt and pepper. The cream is best eaten the same day; it will discolor overnight.
To grill the bread, use a grill pan or grill, right before serving. Use a paper towel to rub a light coating of olive oil in the grooves of the pan and heat it over hight heat if using a grill pan. Cut the bread into sturdy slices and brush it with a light layer of olive oil on each side. Lay the slices in a single layer and toast until they crisp nicely with dramatic grill marks, about 2 or 3 minutes. Flip and grill the other side of each slice.
Spread a liberal layer of the horseradish cream on each piece of bread. Arrange a pretty pile of beef slices atop the cream, drizzle with olive oil, and sprinkle with crunchy salt and a few grinds of black pepper.
