Make the Twinkies
Generously coat a nonstick 8-cup éclair pan with the vegetable oil. Preheat the oven to 350°F.
Sift the flour, baking powder, and salt into a small bowl. Set aside.
Using a stand mixer fitted with the whisk attachment, beat the egg yolks and 1⁄2 cup of the sugar on medium-high until pale yellow and doubled in volume, 4 to 5 minutes. Using the dull side of a knife, scrape the vanilla bean seeds from the pod into the mixture. (Reserve the pod for another use.) Reduce the speed to low, add the vanilla extract and sour cream, and mix until incorporated. Scrape the mixture into a large bowl and set aside.
Wash and dry the mixer bowl and whisk attachment. Using the stand mixer with the clean bowl and whisk attachment, whisk the egg whites with the remaining 1⁄2 cup sugar on medium-high until stiff peaks form, 3 to 4 minutes. Gently fold half of the dry ingredients into the yolk mixture, and then fold in the remaining dry ingredients. Gently fold in the egg whites just until combined, being careful not to deflate the batter.
Fill the éclair cups just a bit more than half full. Bake until springy to the touch and light golden brown, 9 to 12 minutes. Cool in the pan for 1 minute only, and then remove from the pan, using a knife to loosen the sides. Wipe out the pan, oil again, and repeat, using the remaining batter. Cool the cakes completely before filling.
Make the pudding
In a small bowl, whisk the eggs, vanilla, cornstarch, and 1⁄2 cup of the cream together. Set aside.
In a large nonreactive saucepan, combine the granulated sugar, corn syrup, water, and lemon juice and bring to a boil over medium-high heat. Reduce the heat to low and whisk in the molasses, butter, and miso. Simmer for a few minutes, and then add the milk and remaining 1 cup cream. Increase the heat to medium, add the egg mixture, and bring back to a boil, whisking vigorously. Reduce the heat to low and continue whisking until the mixture is bubbly and thick, about 5 minutes.
Remove the pudding from the heat, and strain through a fine mesh sieve into a glass bowl. Cover the surface directly with plastic wrap to prevent a skin from forming, and let cool at least 30 minutes.
Fill a squirt bottle or piping bag with the pudding. Turn the cakes over and carefully insert the bottle or piping tip into the flat underside of the cake. Squeeze in three equal squirts to distribute the filling evenly. Turn over and sift powdered sugar on top before serving.
Make Ahead Tips
The pudding can be made up to 1 week ahead and refrigerated, covered.
Photo: Karen Brooks