Slice the trimmed sirloin into 1-inch pieces and chill it in the freezer for 10 minutes. The meat should feel semi-firm at the edges, which keeps the knife from sliding and helps the fat stay neat.

Whisk the sherry vinegar, dry mustard, and egg yolks in a small bowl, then slowly drizzle in the light olive oil while whisking constantly. Continue until the dressing looks thick, smooth, and glossy, with no separated oil around the edges.

Stir the shallots, capers, kosher salt, and about two-thirds of the celery leaves and parsley into the emulsified dressing. The capers and herbs should be evenly suspended through the creamy binder.

Finely hand-chop the chilled beef, or pulse it in four separate batches 3 to 4 times in a food processor fitted with an S-blade. Stop when the beef has distinct small pieces rather than a sticky, paste-like texture.

Use clean hands to fold the beef and dressing together quickly, then shape it with a 3 3/4-inch pastry ring and finish with the reserved herbs and lemon zest. The finished tartare should look bright crimson with a light, even sheen over each piece.