Flank steak crostini appetizers with blue cheese and blueberry caramelized onion jam

Blue Cheese and Steak Crostini with Blueberry and Caramelized Onion Jam

Course: Appetizer
Prep Time: 20 minutes
Cook Time: 1 hour 10 minutes
Total Time: 1 hour 30 minutes
Servings: 24 crostini
Author: Caroline Lindsey
Blue cheese and flank steak crostini topped with blueberry balsamic and caramelized onion jam are hearty and savory with just a touch of sweetness! Try these easy, decadent appetizers for your next gathering!
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For the crostini

  • 1 baguette or long Italian or French loaf not too crusty!
  • 1/4 cup olive oil
  • kosher salt

For the steak

  • 1 lb flank steak
  • 1 tbsp olive oil
  • kosher salt and pepper

For the blueberry and caramelized red onion jam

  • 1 tbsp olive oil
  • 1 medium red onion diced (about 2 cups)
  • several sprigs fresh thyme
  • 1/2 tsp kosher salt
  • 1/4 tsp freshly ground pepper
  • 2 cups blueberries
  • 2 tbsp balsamic vinegar
  • 1/4 cup honey
  • 2 tbsp brown sugar
  • 1/4 cup red wine
  • 1 tsp lemon juice

For assembling

  • 4 oz wedge blue cheese
  • arugula microgreens can use other microgreens, radish sprouts, or baby arugula


  • Follow instructions for making Savory Blueberry and Caramelized Onion Jam. Allow at least an hour to make jam and let it cool before beginning the next step. This step can be done several days in advance.
  • Preheat oven to 375 degrees Fahrenheit. Slice bread into 1/3-1/2-inch slices and arrange on a sheet pan. Brush slices with olive oil and sprinkle with kosher salt. Bake for 7-10 minutes, or until crispy on top. Set aside crostini. Note: Crostini may not brown, and that's okay! Don't keep baking it until it's brown, or it will end up far too crunchy. Alternately, you can put it under the broiler for a 2-4 minutes instead of baking at 375 to get more browning on top, if that's important to you! 
  • Turn oven to broiler and set top rack to about 4-6 inches away from the heating element (I do the second from the top position on mine). Pat flank steak dry with paper towels. Then drizzle olive oil on both sides of steak and rub in gently. Sprinkle on both sides with kosher salt and black pepper and put steak on a sheet pan.
  • Cook steak under the broiler for about 5 minutes per side, until medium rare. Then let it rest for another 5 minutes so it will stay juicy when you slice it! Slice as thinly as possible against the grain.
  • Top crostini pieces with several (2-3) slices of steak, folded and draped decoratively. Then add a couple blue cheese crumbles, a small dollop of jam, and a pinch of microgreens. Note: Taste one first to make sure the ratios are all good before you make the whole batch! It's easy to overwhelm the steak with too much blue cheese or jam. If using baby arugula instead of microgreens, layer them on the bottom of the crostini before adding the steak.
  • Enjoy along with wine and a cheese board!