In a large bowl, whisk together the flour, baking soda, cream of tartar and salt. Set aside.
In another bowl, whisk together the oil and sugar. Add in the eggs and peanut butter and whisk again, but be sure to not over mix.
Dump the dry ingredients, banana and chips on the wet ingredients and switching to a rubber spatula or wooden spoon, gently fold the ingredients together just until a few streaks of flour remain.
Scoop one large spoonful (we actually use a cookie scoop ) into the bottom of the muffin wells and place a dollop of the frozen nutella in the batter. (See note for options) Cover with batter up to 2/3 high in the well.
Place a little nutella on top of the batter and using a small knife, starting at the outside edge of the batter, swirl through and around the nutella.
Allow to rest in the pan for 8-12 minutes before baking. See note.
Bake at 350 for 25 minutes or 12-16 minutes for regular muffins. The muffins are done when lightly golden and the middle springs back up when you touch the top.
Once the muffins are done, open the oven door, turn off the oven and let the muffins rest for 2 minutes, no longer, before carefully setting it on the counter for a few more minutes to cool.