Preparation

Position a rack in the center of the oven, and preheat to 375°F. Line a standard 12-cup muffin tin with paper or foil liners.

In a medium bowl, whisk together the flours, sesame seeds, baking powder, baking soda, and salt.

In a large bowl, beat the eggs and sugar using an electric mixer on medium-high speed until lightened and quadrupled in size, about 3 minutes. Beat the bananas, oil, and tahini into the egg mixture on medium-high until well combined, about 30 seconds more.

Add the dry ingredients, reserving the bowl, to the wet ingredients. Beat on low speed until just combined.

Remove 1-1/4 cups of the batter to the reserved bowl. Mix the cocoa powder into that reserved batter.

Using a cookie scoop or a measuring spoon, scoop 3 Tbs. of the original batter into each muffin cup. Top with a dollop of the chocolate batter, and use a kitchen knife or wooden skewer to swirl the two batters, swooping from bottom to top.

Bake until a toothpick inserted in the center of a muffin comes out clean, 17 to 20 minutes. Place a banana slice on top of each muffin, if using. Cool in tin on a wire rack 10 minutes. Serve warm or at room temperature.