Lemon Curd

1. Add lemon zest, juice, sugar, and eggs to a double boiler. Whisk until blended. Add butter to the ingredients and set over a saucepan of simmering water, whisking continuously. The double boiler provides precise temperature control, so the mixture stays smooth while it thickens for about 20 minutes.

Batter

1. Combine in a large bowl flour, sugar, and salt. In a measuring cup, whisk together eggs, milk, and vanilla. Gently whisk wet ingredients into dry ingredients until everything is thoroughly blended. Cover and let stand at room temperature for 1 hour or chill in the refrigerator for 2 to 3 hours.
2. Preheat the oven to 450° about 20 minutes before the end of resting time. Put a 10-inch cast iron skillet in the oven when very hot to preheat for 10 minutes. 
3. Remove the hot skillet and work quickly. Pour in melted butter and cover the spattering skillet while swirling the butter to coat the pan. 
4. Whisk the batter one more time before pouring it into the skillet. 
5. Scatter blueberries over the top and place the pan in the oven. 
6. Bake for about 15 minutes until the Dutch baby is puffed up and golden brown around the edges and set in the center. 
7. Dust with powdered sugar. 
8. Serve each slice of Dutch baby with a dollop of lemon curd.