Turn oven on to 400 degrees. Dump the walnuts onto a baking sheet and slide them into the oven to toast slightly while you're doing the rest of the prep. Set the timer for 10 minutes so you don't forget about them. Take them out and let them cool a bit before you chop them.

Mix or whisk the wet ingredients, including the carrot and apple, together in another bowl, being sure to add the water here if you used the buttermilk powder. (You don't absolutely have to do this separate bowl step, but it's hard to get things mixed evenly if you don't.) As this point you should have your walnuts chopped, so mix those into the dry ingredients. Then pour the wet mixture on top of the dry ingredients and use a spatula to get everything combined. Be sure to get all the dry ingredients mixed in. It's surprisingly hard to do this, so make sure you're going all the way to the bottom of the bowl and scraping up. Stop as soon as you don't see any more streaks of the flour mixture. You'll notice that the batter starts getting bubbly as soon as you combine the two sets of ingredients. That's the baking powder starting to work, and you don't want to deflate things too much, so work with a light hand.

Spray your muffin pans with baking spray or use foil or paper liners. Portion out the batter among the 14 cups. Bake until lightly browned on top and a toothpick comes out clean, 15-20 minutes. Let cool in the pans for 5 minutes before taking them out and putting on a cooling rack. Good warm or at room temp. Don't forget the butter!