- Preheat the oven to 400°F. Line the wells of a muffin pan with papers and grease the insides of the papers.
- To make the batter: In a large bowl, mix together the yogurt, egg, oil, and mashed banana. Stir in the white whole wheat flour.
- Place a sifter or strainer over a medium bowl. Sift the sugar, malted milk powder, all-purpose flour, baking powder, baking soda, and salt into the bowl. Whisk to combine, then add to the wet mixture and stir until the batter is evenly moistened. Stir in the chips (if using). Scrape the bowl to make sure there are no dry spots.
- To make the swirl: Whisk the cocoa, malted milk powder, confectioners’ sugar, and ClearJel through a strainer into a medium bowl. In a microwave-safe bowl, heat the butter and milk together until the butter is melted, about 1 minute at half power. Add to the dry mixture and whisk until smooth. Place the mixture in a disposable pastry bag and snip a 1/4” opening at the bottom.
- To assemble: Scoop the batter by the 1/4 cup into the wells of the prepared muffin pan (each well should be about three-quarters full). Bury the tip of the filled pastry bag 1” deep in the scooped muffin batter and squeeze out two to three dollops under the surface. Repeat with each muffin. Take a small knife or pointed small spatula and draw it down through each muffin, then up and over once or twice to create the swirl.
- Bake the muffins for 18 to 20 minutes, until the tops spring back when lightly touched and a paring knife inserted in the center of a muffin comes out clean.
- Remove the muffins from the oven and cool in the pan for 5 minutes before carefully tipping them onto a rack to finish cooling completely.
- Store any leftovers, well wrapped, at room temperature for several days; freeze for longer storage.