A traditional 12-inch skillet may be used in place of the nonstick skillet; coat it lightly with vegetable oil spray before using. Prepare the topping while the Dutch baby bakes.

FOR THE DUTCH BABY: Whisk flour, sugar, and salt together in large bowl. Whisk milk and eggs together in second bowl. Whisk two-thirds of milk mixture into flour mixture until no lumps remain, then slowly whisk in remaining milk mixture until smooth.

Adjust oven rack to lower-middle position. Melt butter in 12-inch ovensafe nonstick skillet over medium-low heat. Add batter to skillet, immediately transfer to oven, and set oven to 375 degrees. Bake until edges are deep golden brown and center is beginning to brown, 30 to 35 minutes. Gently transfer Dutch baby to cutting board. Let cool for at least 5 minutes. (Dutch baby will deflate.)

FOR THE TOPPING : while Dutch baby rests, combine ½ cup water, shallot, and ¼ teaspoon salt in small bowl. Stir well and let sit for 5 minutes. Drain shallot and discard liquid; set aside. Combine sour cream, caper brine, 1½ teaspoons dill, and remaining ¼ teaspoon salt in second bowl.

Using vegetable peeler, shave cucumber lengthwise into ribbons on 1 side until you reach seeds. Turn cucumber 180 degrees and repeat on other side; discard core.

Spread sour cream mixture evenly over Dutch baby. Arrange smoked salmon on top of sour cream. Scatter cucumber ribbons over Dutch baby. Sprinkle with shallot, capers, and remaining 1½ teaspoons dill. Cut into wedges and serve.

For a Lush, Custardy Dutch Baby, Start in a Cold Oven