Japanese Soufflé Pancakes

Whisk together flour, baking powder, and salt in a medium bowl. Whisk together 6 egg yolks, milk, and vanilla in a large bowl. Gradually sift flour mixture into yolk mixture; whisk until smooth. Chill at least 20 minutes or up to overnight (about 8 hours).

Place 8 egg whites in bowl of a heavy-duty stand mixer (save remaining yolks for another use). Freeze until egg whites are partially frozen, about 15 minutes. Add lemon juice to egg whites, and beat with a whisk attachment on medium speed, gradually adding sugar, until glossy and stiff peaks form, 6 to 8 minutes. Using a hand whisk, gently fold egg white mixture into chilled batter, in 2 additions, until just incorporated. Using a rubber spatula, finish folding, if needed, to fully incorporate. Transfer half of batter to a large piping bag or ziplock plastic bag with a 1-inch hole cut in one corner. Keep remaining batter chilled, uncovered, while cooking the first batch.

Preheat a large electric griddle to 300°F. Lightly grease griddle with butter. Pipe 4 cone-shaped mounds of batter, about 3 inches wide on bottom and 3 inches tall (do not layer the batter), leaving at least 2 inches between mounds. (Make sure pancakes are close enough so that all 4 mounds will fit under the aluminum pan.) Spoon 2 tablespoons water on surface of the griddle around the pancakes. Immediately cover pancakes with the inverted aluminum pan to steam-griddle them. Cook until top of batter looks dry and bottom of pancakes are lightly browned, 5 to 6 minutes. Using 2 thin spatulas (such as fish spatulas), carefully flip pancakes. Spoon 2 tablespoons water on surface of griddle around pancakes. Cover with inverted aluminum pan, and cook until pancakes are set, 5 to 6 minutes. Transfer pancakes to serving plates. Repeat process with remaining batter and water. Top with butter and maple syrup. Sprinkle with powdered sugar. Serve immediately.