Whisk the ricotta, heavy cream, and zest if using in a mixing bowl until combined. Add in the ¼ teaspoon of salt and a few cranks of black pepper. Taste the ricotta and adjust the seasoning as necessary.
Preheat the oven to 425°F. Lay the baguette slices out on a sheet pan and drizzle each with a little olive oil. Toast until they are golden brown, about 6 minutes.
In a large bowl, toss the squash with 2 tablespoons of olive oil and the maple syrup. Season with salt and pepper. Arrange in a single layer on a rimmed baking sheet. Roast, tossing occasionally, until squash is golden and tender, 25-30 minutes. Let cool on sheet.
Heat the remaining 2 tablespoons oil in a pan over medium-high heat. Working in batches, add sage leaves and cook until edges begin to curl and turn dark green, 1-2 minutes. Using a slotted spoon, carefully transfer to paper towels to drain.
Spread the ricotta mixture over the toasted baguette slices. Add a spoonful of the roasted butternut squash and crispy sage leaf to each crostini, then drizzle with olive oil and season with freshly cracked black pepper and flaky sea salt.