Roasted Grape and Ricotta Toasts

Heat the oven to 200°C (400°F) and line a large rimmed sheet pan with parchment. Remove the grapes from their stems, wash and dry them well. Toss the grapes in a medium bowl with 2 teaspoons olive oil, the balsamic vinegar, rosemary and 1/8 teaspoon salt. Spread them on one half of the pan in a single layer.

Roast for about 18 to 22 minutes, until several grape skins split and the fruit softens and releases juice. Watch the pan near the end so the juices do not scorch. Carefully scrape the grapes and all pan juices into a heatproof bowl. Leave the oven on.

Brush both sides of the sourdough slices with the remaining 2 teaspoons olive oil, using about 1/2 teaspoon per slice. Place the slices on the same lined pan in one layer. Toast for about 5 to 7 minutes, turning halfway, until the edges are crisp and the centres are warm. Watch closely because bread thickness and ovens vary.

Meanwhile, stir the ricotta and lemon zest in a small bowl with the remaining 1/8 teaspoon salt and the black pepper. Spread about 1/4 cup of the ricotta mixture on each warm toast. Divide the roasted grapes and their juices among the four toasts, then scatter 1 tablespoon chopped walnuts over each. Serve immediately while the toast is crisp.

For make-ahead preparation, refrigerate the roasted grapes promptly in a shallow container within 2 hours, leaving them uncovered or loosely covered until cooled, then cover. Refrigerate the ricotta separately in a covered container. Use both within 2 to 3 days. Toast fresh bread when ready to serve. If reheating the grapes, heat only the portion needed to 74°C (165°F), then assemble with chilled ricotta. Do not store assembled toasts if crisp bread is important.