Preheat the oven to 350°F. Grease a bundt pan and set aside.
In a medium bowl, whisk the flour, baking powder, baking soda, and salt together. Set aside.
2 ¾ cups (407g) gluten free flour blend, 2 teaspoons baking powder, ½ teaspoon baking soda, ½ teaspoon salt
Using a hand mixer or a stand mixer with the paddle attachment, cream the butter and sugar. Add the Greek yogurt and vanilla extract and mix until combined.
1 cup (226g) unsalted butter, 1 ½ cups (300g) granulated sugar, 1 cup (227g) Greek yogurt, 2 teaspoons vanilla extract
Add the dry ingredients and mix on low speed. Add the buttermilk and continue beating until combined.
½ cup (120ml) buttermilk
Remove a little less than half of the cake batter and place in a separate bowl. Mix in the melted chocolate until thoroughly combined to make the chocolate batter.
¾ cup (128g) chocolate chips
Scoop cake batter into prepared pan, alternating between vanilla and chocolate batter. Use a rubber spatula to smooth out the top, then use a knife or wooden skewer to swirl. Bake for 50-55 minutes or until a toothpick inserted into the center comes out clean. Allow the cake to cool in the pan for 20 minutes before inverting onto a plate or stand.