Preheat oven to 350 degrees
Using 2 tablespoons of room temperature butter, grease 1 large soufflé dish or 4 smaller soufflé dishes and then dust 1/4 cup of granulated sugar in the dish(es), ensuring that all interior surfaces of the dish(es) have been buttered and covered in sugar and then set the prepared dishes aside
In a small saucepan, bring 1 cup of whole milk just to a simmer and then remove the pan from the heat
In a medium mixing bowl, combine 1/3 cup of granulated sugar, 1/3 cup of all-purpose flour, 1/3 cup of whole milk, 4 egg yolks and 1 table spoon of lemon zest into a smooth batter
Slowly add a bit of the hot milk into the batter while whisking constantly. Continue to add a bit more at a time until all of the hot milk has been combined with the batter and everything is fully incorporated
Transfer the batter back into the saucepan and return it to medium heat. Whisk constantly until the batter thickens (about 60-90 seconds)
Remove the batter from the heat and add 2 tablespoons of room temperature butter. Whisk until the butter has melted and combined with the batter. Set the batter aside to cool for 10 minutes
In a medium bowl, beat 4 egg whites until foamy. Add 2 tablespoons of sugar and continue beating the egg whites until stiff, shiny peaks form
Once the batter has cooled for 10 minutes, add 2 teaspoons of vanilla extract and several drops of lemon extract and whisk to combine
Add 1/4 of the whipped egg whites to the batter and gently fold to combine. Continue adding egg whites until everything is combined and smooth. Be careful not to overmix
Transfer batter into soufflé dish(es) filling it to the top
Smooth the tops with the back of a knife
Bake at 350 degrees for approximately 28 minutes. The soufflé should rise tall and the top should be crusted and slightly golden. Avoid opening the oven door until the soufflé is ready to be removed from the oven
Dust with confectioners sugar and serve immediately