Preheat oven to 350°F. Arrange squash on a greased baking sheet, cut sides down, and bake until tender, about 45 minutes. Set aside to let cool then transfer 1 1/2 cups of the flesh to a food processor. (Save any remaining flesh for another use.)
Heat oil in a large skillet over medium high heat. Add shallots, salt and pepper and cook until golden, about 5 minutes. Meanwhile, brush bread all over with oil, arrange on a large baking sheet in a single layer and toast in the oven, flipping halfway through, until just golden and crisp, 8 to 10 minutes total.
Add shallots and almond butter to food processor with squash and purée until smooth. Spread over warm crostini and serve.
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