Adjust oven rack to the middle position and preheat to 350 degrees F . Toast pecans on a half-sheet pan until golden brown, about 10 minutes, then let cool completely. Meanwhile, peel, trim, and core the pineapple and measure 5 ounces fruit into the jar of a blender, or a tall, narrow jar if using an immersion blender. If you like, reserve the pineapple scraps to make fresh pineapple syrup . Peel banana and measure out 3 ounces fruit to add along with the pineapple. Blend until smooth. Use purée immediately or refrigerate up to 3 days and bring to about 70 degrees F before use.
