Preheat the oven to 450°F. Place the oven rack in the lowest position. Generously grease a popover or muffin pan.
In a blender, combine 2 eggs (room temperature) and 1 cup milk (room temperature). Blend until smooth.
Add 1 cup all-purpose flour to the blender and blend until there are no lumps, scraping down the sides if needed.
Transfer the batter to a bowl and stir in 1 1/2 tablespoons Basil and Walnut Pesto and 3 tablespoons grated Parmesan until evenly combined.
Place the greased pan in the hot oven for 2 minutes to preheat. Using oven mitts, remove the hot pan from the oven.
Pour the batter into each cup of the hot pan, filling each about half full. Return the pan to the oven.
Bake at 450°F for 20 minutes without opening the oven door. Then reduce the oven temperature to 350°F and bake an additional 10–15 minutes, until the popovers are lightly browned and puffed.
Remove the pan from the oven and let the popovers cool briefly in the pan before removing and serving.