Brown Butter Banana Cupcakes with Vanilla Custard

Steps

1. Make the custard first so it can chill: in a saucepan whisk 1 egg (one third of the eggs), the granulated sugar and the cornstarch until smooth, then whisk in the whole milk.
2. Cook over medium heat, whisking constantly, until bubbling and thick and the custard reaches at least 160°F (71°C), about 5 minutes.
3. Off the heat, whisk in two thirds of the vanilla and 15 g of the butter (a small portion of the butter). Scrape into a bowl, press plastic wrap onto the surface and chill at least 2 hours, until cold and set.
4. For the cupcakes, melt the remaining butter in a small pan over medium heat, swirling, until it smells nutty and the solids turn golden brown, 5 to 6 minutes. Pour into a large bowl and cool 10 minutes.
5. Preheat the oven to 350°F (175°C) and line a 12-cup muffin pan with paper liners.
6. In a medium bowl whisk the flour, baking soda, baking powder, salt and cinnamon.
7. Into the browned butter whisk the brown sugar, then the remaining 2 eggs, the mashed banana, the Greek yogurt and the remaining third of the vanilla until smooth.
8. Fold the flour mixture into the banana mixture just until no dry streaks remain.
9. Divide the batter among the liners, filling each about three quarters full.
10. Bake 18 to 22 minutes, until the tops spring back and a toothpick in the center comes out clean.
11. Cool in the pan 5 minutes, then on a rack until completely cool, about 1 hour.
12. Whisk the chilled custard smooth and spoon it into a piping bag. Cut a small cone from the top of each cupcake with a paring knife, pipe in the custard, and replace the cones.
13. Dust the tops with the powdered sugar through a sieve and serve; refrigerate leftovers.