Blueberry Swamp Pie

Directions

1. Heat the oven to 375°F with a rack in the lower third of the oven (preferably with a baking steel or stone on it). Stir all the ingredients for the streusel together to combine, then add the butter and cut it into the mixture until it forms large clumps.
2. In a medium bowl, toss the blueberries with the lemon zest and juice. (If using vanilla extract instead of vanilla bean, add here, too.)
3. In a small bowl, mix the sugar and vanilla bean scrapings with your hands, rubbing the two together to disperse the seeds. Stir in the flour and salt, then sprinkle this mixture over the blueberries, stirring until well combined.
4. Pour this mixture into the cooled par-baked pie crust and arrange in an even layer. Sprinkle the streusel evenly over the top of the pie.
5. Transfer the pie to the oven (on top of the steel/stone, if using). Bake until the crust is deeply golden and the berries are juicy and bubbly, 35 to 40 minutes.
6. Just before the pie reaches the 35 minute mark, make the custard filling. In a medium bowl, whisk the cream, brown sugar, egg, and vanilla to combine. When the pie reaches the doneness listed in step 4, pull out the oven rack and gently pour the cream mixture all over the surface of the bubbling pie. If the cream looks like it’s going to overflow over the edge of the crust, make a small hole with a paring knife to give you a spot to pour the custard, then slowly pour the custard into the well. Don’t go too fast, or it will overflow instead of sinking into the pie.
7. Return the rack to the proper place and continue to bake until the custard is set around the edges but slightly jiggly in the center, 10 to 15 minutes more. Let cool completely before slicing and serving.