Wrap the trimmed beef tenderloin in plastic wrap and place it in the freezer for 20 minutes. This firms up the meat, making it much easier to chop into precise, uniform cubes.

Preheat your oven to 375°F (190°C) to prepare the crostini. Arrange baguette slices on a baking sheet, brush lightly with olive oil, and bake for 8-10 minutes until golden and crisp. Upon removing from the oven, lightly rub the toasted slices with the cut side of the garlic clove. Set aside to cool.

Remove the beef from the freezer. Using a very sharp chef's knife, slice the beef into 1/8-inch thick slices. Cut those slices into 1/8-inch strips, and finally crosshatch them into uniform 1/8-inch cubes. Place the chopped beef into a chilled mixing bowl.

In a separate small bowl, whisk together the Dijon mustard, Worcestershire sauce, hot sauce, and olive oil.

Add the finely minced shallot, capers, cornichons, and parsley to the chopped beef. Pour the dressing over the top and gently fold everything together until evenly distributed. Season with flaky sea salt and freshly ground black pepper to taste. Do this immediately before serving so the acid doesn't 'cook' the meat.

To plate, place a ring mold in the center of a chilled plate. Spoon a quarter of the beef mixture into the mold, gently pressing it down to form a flat, even layer. Remove the mold.

Create a small, shallow indentation in the top center of the tartare patty. Carefully nestle one raw quail egg yolk into the indentation. Repeat for the remaining portions. Serve immediately with the prepared crostini.