6 tablespoons unsalted butter
4 large eggs
3 tablespoons sugar
1/2 teaspoon kosher salt
3 tablespoons whole milk
1/2 cup plus 1 tablespoon all-purpose flour
Nonstick cooking spray
In a saucepan, cook the butter over moderate heat, swirling the pan, until the milk solids turn deep brown, 5 minutes. Let cool.
In a bowl, whisk the eggs with the sugar and salt until pale. Whisk in the milk. Whisk in the flour and the brown butter until the batter is very smooth and uniform in color.
Pour the batter into the canister of a 1 pint dispenser. Seal the siphon and charge it with one cream (N2O) cartridge. Shake the siphon vigorously.
Poke 3 holes around the side of eight 8-ounce wax-coated paper cups and coat the interiors with cooking spray. Hold the siphon upside down and insert the nozzle into one of the cups. Gently press the handle to dispense the batter; use a circular motion to evenly fill one-third of the cup. Set the cup in a microwave oven and cook on high for 45 seconds, until the cake is fluffy and risen. Invert the cup onto a plate and let stand for at least 1 minute. Repeat with the remaining batter and cups. Remove and discard the cups. Serve right away.