Preheat your oven to 425°F (220°C). This high temperature is crucial for achieving the perfect puff in your popovers.
Lightly grease your popover pan with cooking spray or melted butter to prevent sticking.
In a mixing bowl, whisk together the 2 eggs and 1 cup of milk until well combined.
In a separate bowl, whisk together the 1 cup of all-purpose flour and a pinch of salt (optional).
Gradually add the dry mixture into the wet ingredients, whisking until just combined.
Gently fold in the 1 1/2 tablespoons of basil and walnut pesto and the 3 tablespoons of grated Parmesan cheese into the batter.
Pour the batter into the prepared popover pan, filling each cup about halfway.
Place the pan in the preheated oven and bake for about 20-25 minutes, or until the popovers are golden brown and puffed up.
Once baked, remove the popovers from the oven and let them cool for a few minutes in the pan before transferring them to a wire rack.