Having a dinner party?  Start your guests off with this delicious walnut crostini.  The sweetness of the caramelized onions really compliments the sharp flavor of the arugula.

Preparation

To prepare the caramelized onion, melt the butter in a medium saucepan over medium-low heat. Add the olive oil and onion, season lightly with salt and pepper and stir to combine.

Cook for 20–30 minutes, or more, stirring frequently—it is okay if the onions brown lightly, which gives them color and sweetness, but don’t burn them. When done, the onions will have reduced to about ¼ cup and be a pale golden color. Transfer to a small bowl and set aside.

To prepare the seasoned walnut spread, wrap the carrot, celery, shallot and bay leaf in a double thickness of cheesecloth and tie the bundle securely with twine. Put in a medium saucepan, pour in the milk and season with ¼ teaspoon salt and 1/8 teaspoon pepper. Bring to a simmer over medium-high heat. Add the walnuts, reduce the heat, and poach in the simmering milk for 18–20 minutes, stirring once or twice.

Strain, reserving the milk. (Discard the cheesecloth bundle.) While the walnuts are still warm, put them in a food processor. Add 1/3 cup of the reserved milk and puree. Add additional milk by tablespoons, until the mixture is smooth and spreadable. Season to taste with salt and pepper, transfer to a bowl and set aside. (Any remaining milk may be used in a soup or sauce.)

To prepare the crostini, brush the baguette slices lightly with olive oil, put them in a single layer on a baking sheet, and place in a preheated 350ºF oven for about 5 minutes, to dry and crisp. Remove from the oven and gently rub each slice with garlic.

Spread about 1 tablespoon of seasoned walnut mixture on each crostini. In a small bowl toss the arugula with 1 tablespoon olive oil, then season lightly with salt and pepper. Drape a few leaves of arugula over each crostini and top with about 1/2 teaspoon caramelized onions.