For the batter
2 cups (280 g) all-purpose gluten-free flour
1 teaspoon xanthan gum (omit if your blend already contains it)
3/4 teaspoon kosher salt
1 teaspoon baking powder
1/2 teaspoon baking soda
2/3 cup (133 g) granulated sugar
8 tablespoons (112 g) virgin coconut oil, melted and cooled
2 eggs (100 g, weighed out of shell) at room temperature, beaten
1 teaspoon pure vanilla extract
2/3 cup (150 g) thick non-dairy plain yogurt, at room temperature (my favorite brand is Anita coconut yogurt)
1 cup (200 g) ripe bananas, peeled and mashed lightly (from about 2 medium-size bananas)
For the swirl
2 tablespoons (28 g) virgin coconut oil, melted
1/3 cup (67 g) granulated sugar
2 teaspoons ground cinnamon
1/8 teaspoon kosher salt
Preheat your oven to 350°F. Grease a standard 9 x 5 inch loaf pan, and set it aside.
In a large bowl, place the flour, xanthan gum, baking soda, baking powder, salt and sugar, and whisk to combine well. Add the coconut oil, eggs, vanilla, then the yogurt, mixing until just combined after each addition. Add the mashed bananas and mix them carefully into the batter, taking care not to further mash the bananas. Transfer half of the banana batter to the prepared loaf pan and spread it into an even layer with a wet spatula. Set both aside briefly.
Make the swirl. In a small bowl, place all of the swirl ingredients and mix to combine well. It will be a thick mixture. Place about one half of the swirl mixture on top of the batter already in the loaf pan and spread it gently into an even layer. Top with the remaining banana batter and spread that with a wet spatula into an even layer. Finish with the remaining swirl batter and spread again gently into an even layer. With a butter knife held perpendicular to the bottom of the loaf pan, swirl the batter from one short side to the other of the pan, back and forth in looping pattern (watch the video for a visual demonstration!). Smooth the top of the swirled batter into an even layer once more.
Place the pan in center of the preheated oven and bake for 45 minutes. The loaf should be until golden brown on top, and mostly firm toward the center. Lower the oven temperature to 325°F and continue to bake until completely firm when pressed lightly in the center, another 10 to 15 minutes. Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely before slicing and serving. Leftovers can be wrapped very tightly and stored at room temperature for up to 3 days, and frozen for longer storage.