Adjust oven rack to middle position and heat oven to 450 degrees.

Brush surface and sides of a large (12 in.) skillet liberally with vegetable oil.

Place skillet on oven rack and heat until oil is shimmery, about 10 minutes.

In a large bowl, combine flour, cornstarch, lemon zest, and salt.

In another bowl, whisk eggs until frothy and light, about 1 minute.

Whisk milk, melted butter and vanilla into eggs until incorporated.

Whisk one-third of the milk mixture into the flour mixture until no lumps remain.

Slowly whisk in remaining milk mixture until smooth.

Carefully pour batter into heated skillet.

Bake until edges of Dutch Baby are deep golden brown and crisp, about 15 -20 minutes.

Transfer skillet to wire rack.

Sprinkle with lemon juice (if desired) and confectioner's sugar.

Cut into wedges.

Serve alone or with berries and whipped cream.