1 pound asparagus, trimmed
1 large leek (white and light green part only)
4 teaspoons olive oil, divided
1 clove garlic, roughly chopped
1/4 cup ricotta cheese
3 tablespoons lemon juice
2 teaspoons lemon zest (optional)
Salt and pepper
1/2 pound prosciutto
1 loaf of ciabatta, baguette, or other artisan loaf, sliced thinly
Melted butter or olive oil
Bring a pan of water to a boil over high heat. Add the asparagus and cook until tender and bright green, about 5 minutes. Remove the asparagus from the pan and place in an ice bath (or run under cold water) to stop the cooking. Pat dry.
Slice the leek in half lengthwise and set aside one of the halves for another use. Chop the remaining half. Heat 2 teaspoons of olive oil over medium heat in a skillet. Add the chopped leeks and garlic, season with salt and pepper, and cook until soft but not brown, about 6 to 8 minutes. Set aside to cool.
Roughly chop the cooled asparagus. Combine the chopped asparagus, the leek mixture, and the ricotta cheese in the bowl of a food processor. Pulse until combined. Add the lemon juice, lemon zest, and remaining 2 teaspoons of olive oil. Purée until smooth, then taste and add salt and pepper if needed.
At this point, the asparagus spread can be refrigerated until ready to use, overnight or up to 3 days.
When ready to serve, spread the slices of bread on a parchment-lined baking sheet and brush with melted butter or olive oil. Toast under the broiler for a minute or two until the tops of the toasts are golden and the edges are crunchy — watch the toasts carefully as they can burn easily.
To serve, spread a dollop of asparagus puree on each slice of bread, then top with a piece of prosciutto.