-
Preheat the oven to 350 F. Grease and flour a 9 inch bundt pan. Set aside.
-
Whisk together the flour, potato starch, baking powder, baking soda and salt. Set aside.
-
Beat the butter until creamy. Add the sugar and vanilla bean paste and beat until light and fluffy. Scrape down the sides and bottom of the bowl as needed.
-
Add the eggs, one at a time, beating to incorporate after each one. Remember to scrape the sides of the bowl!
-
Using the lowest speed, add the yogurt and flour mixture, alternating, beginning and ending with flour, in 3 and 4 additions, respectively.
-
Scrape 2/3 - 3/4 of the batter into the prepared bundt pan. Use a spatula to smooth the surface level.
-
Mix together the swirl ingredients. Beat them into the remaining cake batter. Scrape this batter on top of the plain batter in the cake pan, trying to keep it in a center line not touching the pan on either side (do not over stress about this though). Using a butter knife, swirl the espresso batter into the plain batter. Do not touch the sides or bottom of the pan.
-
Bake for 45-55 minutes, until the cake is pulling away from the sides of the pan and a cake tester inserted into the center of the cake comes out clean. Cool in the pan for 15 minutes, and then invert onto parchment paper on a cooling rack. Cool completely before slicing or storing in a cake keeper.