Make your crostini by toasting thin slices of good baguette brushed with olive oil and seasoned with salt and pepper. Or buy them—up north, Crooked Tree Breadworks bakes a crisp, perfect herbaceous crostini that makes appetizers a snap. Assemble the crostini just before serving.
To roast the tomatoes, heat the oven to 275 degrees F. Line a sheet pan with parchment and place the tomatoes, cut side up, on the sheet. Drizzle the tomatoes with olive oil and season lightly with salt and pepper. Bake for about 2 hours, until the tomatoes are slightly shriveled and meltingly soft. Remove and cool to room temperature.
Just before serving, stir the labneh to loosen and smooth it out. Dollop 1-2 teaspoons of the labneh on each crostini. Top this with one or two roasted tomatoes, then dust them with za'atar. Make lots! They go fast.... Serve immediately.