Popover-Topped Pot Pie

Heat ¼ cup plus 1 Tbsp. extra-virgin olive oil in a large (14-cup capacity or more) high-sided ovenproof skillet, rondeau, or Dutch oven over medium. Add 12 oz. Yukon Gold potatoes (about 2 large), peeled, cut into ½" pieces, and cook, stirring often, 2 minutes. Add 1 bunch asparagus, trimmed, cut into ½" pieces, 2 medium carrots, peeled, halved lengthwise, cut into ¼"-thick half-moons, 2 celery stalks, thinly sliced, 2 medium shallots, finely chopped, and 1 cup frozen peas and cook, stirring often, until potatoes are not quite fork-tender (a knife inserted into flesh should meet with a little resistance), 15–18 minutes.

Add 6 garlic cloves, finely grated, and ¼ cup (31 g) all-purpose flour; stir until vegetables are coated and no pockets of dry flour remain. Stirring constantly, gradually pour in 2 cups low-sodium vegetable broth and ½ cup dry white wine, then add ⅔ cup heavy cream, 1 Tbsp. Dijon mustard, 1½ tsp. finely grated lemon zest, ⅓ cup finely chopped dill, 1½ tsp. Diamond Crystal or 1 tsp. Morton kosher salt, and ¾ tsp. freshly ground pepper. Bring to a simmer and cook until sauce coats a spoon, about 1 minute. Remove from heat; add more mustard (up to 1 Tbsp.) and season with more salt and pepper if needed. Let sit at least 20 minutes and up to 1 hour to thicken. (Do not stir; you want a slight skin to form.)

Meanwhile, place a rack in middle of oven; preheat to 425°. Blend 5 large eggs in a blender on high speed until light and fluffy. Add 1 oz. Parmesan, finely grated, 1⅓ cups whole milk, ½ tsp. baking powder, remaining 1¼ cups (156 g) all-purpose flour, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, and ¼ tsp. freshly ground pepper; blend on medium speed just until smooth. Stir in remaining 2 Tbsp. finely chopped dill. Tightly cover batter and let sit until filling is ready.

Holding a spoon upside down over filling, gradually pour batter over spoon to cover filling. Bake pot pie until topping is deep golden brown and very puffed, 45–55 minutes.