To make the pumpkin butter: Cook the pumpkin purée in a medium saucepan set over medium-low heat, stirring frequently, until thickened and reduced to 2½ cups, about 20 minutes. Remove from heat and stir in the salt, pepper, maple syrup and butter. (Pumpkin butter can be made several days in advance and refrigerated. Reheat gently before serving.)
To make the pancetta: Preheat oven to 450 degrees. Place a cooling rack on a rimmed baking sheet and arrange the pancetta slices on top. Roast pancetta for 5 minutes, turn over with tongs, and cook another 3 to 4 minutes until cooked through and crisp.
To make the toasts: Set oven to broil. Slice the ciabatta in half lengthwise, then cut crosswise into 1/2-inch-thick slices. Arrange slices on a baking sheet and broil briefly until just beginning to brown (you want the bread warmed and crisped on one side, but still chewy).
To assemble: Smear about 1 tablespoon of pumpkin purée on each toast. Top with a slice of pancetta and sprinkle with minced rosemary or torn sage leaves and sea salt.