Prepare the Steak: Season the flank steak generously with salt, pepper, and half of the minced garlic. Allow it to sit for about 15 minutes to absorb the flavors.
Cook the Steak: In a skillet over medium-high heat, add the olive oil. Once hot, add the steak and sear for about 4-5 minutes on each side for medium-rare (or to your desired doneness). Remove from heat and let it rest for 5 minutes before slicing thinly against the grain.
Toast the Baguette: While the steak is resting, preheat your oven to 400°F (200°C). Arrange the baguette slices on a baking sheet and brush each side lightly with olive oil. Toast for 5-7 minutes or until golden brown.
Prepare the Garlic Butter: In a small saucepan, melt the butter over medium heat. Add the remaining minced garlic and sauté for about 1 minute until fragrant (do not let it brown).
Assemble the Crostini: Take a toasted baguette slice and brush it generously with the garlic butter. Layer a few pieces of the sliced steak on top of the bread, then add a small handful of arugula or spinach.
Finish with Cheese and Glaze: Sprinkle a bit of grated Parmesan cheese over each crostini. Drizzle with balsamic glaze for an extra touch if using.
Serve: Arrange the crostini on a serving platter and enjoy them warm.
Notes
Serve the crostini on a wooden board for a rustic look, garnished with a sprig of arugula or a sprinkle of extra Parmesan.