Rosemary-Garlic Beef Tenderloin Crostini Platter (with Charred Onion Relish)

Blushing-rosy slices of premium beef tenderloin piled onto crisp crostini with a jammy charred onion relish—an effortless, showstopping party “main” people can eat while mingling.

Ingredients

• 1.6–2 kg (3.5–4.5 lb) **center-cut beef tenderloin**, trimmed (ask butcher to tie it)
• 3 tbsp **olive oil**
• 6 cloves **garlic**, finely grated or minced
• 2 tbsp **Dijon mustard**
• 2 tbsp **fresh rosemary**, finely chopped (or 2 tsp dried)
• 1 1/2 tsp **kosher salt**
• 1 tsp **black pepper**
• 2 large **red onions**, thinly sliced
• 2 tbsp **butter**
• 2 tbsp **brown sugar** (or honey)
• 3 tbsp **balsamic vinegar**
• 1/4 cup **water**
• 2–3 **baguettes**, sliced into 1.5 cm / 1/2 in rounds (about 40–50 pieces)
• **Flaky sea salt**, to finish (optional but excellent)

Method

• 1

  Step 1: Season the beef

  Pat the tenderloin very dry. Mix olive oil, garlic, Dijon, rosemary, salt, and pepper into a paste. Rub all over the beef (get into creases). Let sit at room temp 20 minutes while you prep (this helps even cooking).

• 2

  Step 2: Roast to a perfect medium-rare

  Heat oven to **220°C / 425°F**. Place beef on a rack over a tray (or directly on a tray if that’s what you’ve got). Roast **25–35 minutes** until the thickest part reads:

• 3

  Step 3: Make the charred onion relish

  While beef roasts/rests, melt butter in a large skillet over **medium-high**. Add onions with a pinch of salt. Cook, stirring often, until deeply browned with some charred edges, **10–12 minutes**. Add brown sugar, cook **1 minute** until glossy. Add balsamic + water, scrape up browned bits, then simmer **3–5 minutes** until jammy and spoonable. Taste and adjust salt/pepper.

• 4

  Step 4: Toast the crostini

  Reduce oven to **190°C / 375°F**. Arrange baguette slices on trays. Brush lightly with olive oil, sprinkle with salt. Bake **8–10 minutes**, flipping once, until crisp and just golden (you want crunch, not rock-hard).

• 5

  Step 5: Slice and assemble the platter

  Slice beef thinly across the grain. Arrange crostini on a large board/platter. Top each with a slice (or folded ribbon) of beef. Spoon a small dollop of onion relish on top. Finish with a tiny pinch of flaky salt and black pepper.

Tips

• **Serving style (stress-free):** Assemble 10–15 minutes before guests arrive, or set up a “build-your-own” station: crostini + sliced beef + relish in bowls.
• **Doneness insurance:** For a crowd, pull the tenderloin at **52°C / 126°F**; carryover heat finishes it. Overcooked tenderloin is the only real risk—use a thermometer.
• **Make-ahead:** Relish can be made **2 days ahead**; rewarm to loosen. Crostini can be toasted earlier the same day and kept airtight once fully cooled.
• **What to serve alongside:** A big crunchy green salad and a tray of blistered potatoes or roasted vegetables make it feel like a full dinner without complicating service.

Nutrition (per serving, estimate)