Place the trimmed beef tenderloin in the freezer for 15–20 minutes until very firm but not frozen solid; this makes it easier to finely dice. Using a sharp knife, cut the beef into 1/8" (3 mm) dice or finer according to preference. Keep the meat chilled while you prepare the other components.

Combine seasoning

In a chilled bowl, gently combine the diced beef with 1 tsp sea salt, 1/2 tsp freshly ground black pepper, 1 tbsp extra-virgin olive oil, 1 tsp Dijon mustard, 1 tbsp finely chopped capers, 3 finely diced cornichons, and the minced shallot. Add 1 tsp fresh lemon juice and taste; adjust seasoning sparingly. Keep chilled.

Add egg yolk

Just before serving, form portions of tartare using a ring mold or by hand (about 2–3 oz per serving). Make a small well on top of each portion and place one pasteurized egg yolk. If not using pasteurized yolk, you may omit or serve on the side and inform guests.

Chimichurri

While the beef is chilling, make the chimichurri. Finely chop the parsley, cilantro (if using), and oregano. In a small bowl, combine the herbs with 1 minced garlic clove, 1 tsp red wine vinegar, 2 tbsp extra-virgin olive oil, 1/4 tsp red pepper flakes, 1/4 tsp salt, and 1/8 tsp black pepper. Stir well and taste; adjust acidity or salt if needed. Let sit at room temperature for at least 10 minutes to allow flavors to meld.

Reserve about 1–2 tsp of chimichurri per tartare portion to spoon on top; you can also swirl a little on the plate or brush onto crostini.

To Serve

Arrange toasted baguette slices or crostini on a serving board. If desired, lightly brush with 1/2 tsp olive oil.

Place the prepared tartare portions on the board or plates. Spoon 1–2 tsp chimichurri over each tartare mound (or on the side). Garnish with microgreens or chopped chives.

Serve immediately while beef is cold. Provide small spoons or spreaders so guests can mix in the egg yolk and chimichurri as they like.