Warm the coconut oil until liquid. Bring the milk to room temperature, stir in the vinegar, and let it stand for a few minutes to make a quick buttermilk.
Heat the oven to 350°F (175°C). Whisk the coconut oil, buttermilk, brown sugar, egg, and vanilla until smooth. Stir in both flours, baking soda, baking powder, salt, and allspice just until combined, then fold in the apples.
Scoop the batter into a greased or lined muffin tin.
Melt the butter and mix it with the sugar and cinnamon. Spoon the mixture over the muffin tops.
Bake for about 15 minutes, until golden and springy when pressed.
Notes
Add one teaspoon of cinnamon to the batter for a warmer flavor.