Spiced Squash Soup with Pumpkin Seed Pesto

Preheat oven to 400°F.

Make toasts:Trim and discard crusts from bread. Spread 1 side of each slice evenly with butter and season with salt and pepper. Halve slices diagonally to form triangles and arrange, buttered sides up, on a baking sheet. Toast bread, turning once, in middle of oven until golden brown, about 4 minutes. Transfer toasts to a rack to cool.

Make soup:Put squash, cut sides down, in 2 greased shallow baking pans and roast in upper and lower thirds of oven, switching position of pans halfway through roasting, until very tender, about 1 1/4 hours. Cool and scoop out flesh.

Purée squash in batches in a blender with jalapeño, cumin, and broth until very smooth (add additional water as needed to facilitate puréeing).Transfer to a 6- to 8-quart heavy pot and stir in 5 cups water. Simmer, stirring, 10 minutes, then stir in lemon juice, enough water to thin to desired consistency, and salt and pepper to taste.

Serve soup in bowls topped with slices of toast spread with pesto.

Make PestoHeat 2 tablespoons oil in a large heavy skillet over moderate heat until hot but not smoking, then cook pumpkin seeds with salt and pepper to taste, stirring constantly, until seeds are puffed and beginning to pop (some will brown, but do not let all of them), about 4 minutes. Add garlic and cook, stirring, 1 minute. Transfer to a plate and cool completely.

Pulse seed mixture in a food processor with water, cilantro, scallions, and remaining 4 tablespoons oil until mixture forms a coarse paste (not finely ground). Transfer to a bowl and stir in lemon juice and salt and pepper to taste.