Preheat the oven to 375 degrees Fahrenheit, with the middle rack in position.
Mix the flour, milk, heavy cream, vanilla extract, powdered sugar, egg yolks, and rum together until smooth. Whisk the egg whites with a pinch of salt, and when soft peaks form, add the sugar and keep whisking until firm peaks form. Fold the egg whites into the egg yolk mixture.
Place a small amount of neutral oil in your Dutchess over medium-low heat and pour the batter into the pot. Sprinkle with blueberries (reserving some for serving). Cook over medium-low heat until the bottom of the pancake gets lightly golden underneath and starts to bubble on top.
Then place it in the oven, without a lid, for 7 to 9 minutes until cooked through. (It should be light and airy, but not liquidy, when cooked.)
Now for the fun part! Remove The Dutchess from the oven and, using two forks, tear the pancake into large pieces. Dust with powdered sugar (add as much as you want for sweetness, remembering that you will sprinkle a little more over the top when serving). Add a few tablespoons of butter, and place The Dutchess back on the stove over medium heat to caramelize the pancake pieces, constantly moving them around with a spatula for a few minutes.
To serve, lightly dust with powdered sugar and top with fresh blueberries!
Photos by Farrah Skeiky.