Grease a 12-hollow muffin pan with butter. Set oven at 350 deg F or 180 deg Celsius. If you have a convection (fan) oven it's better to use slightly lower heat.
In a mixing bowl, whisk or beat very well together: the pumpkin, peanut butter, honey, oil and eggs. (If you grease the measuring spoon and cup with a little oil it is easier to measure and the peanut butter and honey will slide out).
Mix the dry ingredients in a separate, large bowl, from the flour on down to the sugar, including the spices. Stir well.
Add the wet ingredients to the dry ingredients, and fold in with a spatula or wooden spoon until just mixed and no dry bits remain. Fold in the chopped pineapple.
(If you find the batter is too firm, add a little of the saved pineapple juice to the batter. However, the batter must be soft and sticky, but just firm enough to hold its shape).
With a tablespoon, drop the batter into the greased muffin hollows. You can add heaped tablespoons slightly higher than the hollows. The batter will spread as it bakes.
Bake for 23 - 25 minutes in the centre of the oven, until puffed and golden brown. Turn out on to wire rack to cool.
Serving suggestion: you could mix cinnamon with confectioner's sugar and sift it over the muffins, OR simply serve as is, with butter and jam.