In a medium saucepan, combine 1 cup of hot water and 6 tablespoons of unsalted butter. Stir over medium heat until the butter is completely melted.
Remove the saucepan from heat. Add 1 cup of all-purpose flour, 1 tablespoon of granulated sugar, and a pinch of salt. Stir vigorously until the mixture forms a ball of dough.
Let the dough cool for a few minutes, then add 3 large eggs and 2 egg whites, one at a time, mixing well after each addition until the dough is smooth.
Heat vegetable oil in a deep frying pan or Dutch oven to 350°F (175°C). Transfer the dough into a pastry bag fitted with a large star tip.
Pipe the dough into the hot oil, forming rings about 3 inches in diameter. Fry a few at a time, avoiding overcrowding.
Fry the crullers for about 3-4 minutes on each side until golden brown and puffy. Remove and place on a cooling rack to drain excess oil.
In a mixing bowl, whisk together 1 ½ cups powdered sugar and 2-3 tablespoons milk until smooth to make the glaze.
Dip the tops of the slightly cooled crullers into the glaze, letting excess drip off, then place back on the cooling rack.
Serve the crullers warm with your favorite coffee or tea and enjoy!