Preheat the oven to 375°F and line a 12-cup muffin tin with paper liners. I like to take some coconut oil on my hands and rub it over the top surface of the tin to ensure that if the muffins grow over the edge, they will not stick.
Add the dairy-free butter to the bowl of a stand mixer fitted with the paddle attachment. If you don't have a stand mixer, place the butter in a large bowl and use a hand mixer with beaters. Beat the butter on medium-high speed for 3 minutes, until lighter in colour. Add the brown sugar to the bowl and beat for another 3 minutes, until fluffy and completely dissolved into the butter. Stop to scrape down the sides and bottom of the bowl with a rubber spatula as needed.
Beat in the eggs, one at a time. Then beat in the bananas until broken into small chunks. The batter will look curdled but don't worry. See step-by-step photos in the blog post.
Mix in the dairy-free buttermilk, lemon juice, and vanilla extract. Start on low speed to avoid sloshing.
In a separate bowl, combine all of the dry ingredients: gluten-free flour, almond flour, baking soda, baking powder, and salt. Pour half of the dry ingredients into the wet ingredients and mix until combined, starting on low speed. Add the remaining dry ingredients and beat gently until combined. Stop the mixer and use a rubber spatula to scrape the bottom and sides to mix in any dry spots. The batter will be fairly thick.
Mix the chocolate chips with a teaspoon of gluten-free all-purpose flour before pouring them into the batter. This will help to avoid them sinking straight to the bottom. Incorporate the chocolate chips gently with a rubber spatula.
Use a large ice cream scoop (equal to about ¼ cup measuring cup) to fill the lined muffin tin. Distribute the batter evenly among 12 muffins. Tip: To achieve smooth, round muffin tops, take a spoon and run it under cold water. Dry lightly, then run the back of the spoon over the top of a muffin. This will smooth any spikey bits on the muffin top that could burn. Repeat, rinsing the back of the spoon before each muffin. Sprinkle the tops of the muffins with additional chocolate chips and coarse sugar. This will result in a nice crunchy muffin top.
Bake for 23-25 minutes until a toothpick inserted in a middle muffin comes out clean. Do not open the oven door until at least 20 minutes have elapsed. Allow to cool in the pan for 15 minutes before removing to a wire rack. Enjoy warm or allow to cool completely.