Mix together flour, salt and cardamon in a bowl. Set aside.
Whisk together, milk, lemon zest and the two eggs in another bowl.
Melt one Tbsp butter.
Add flour mixture to egg mixture and stir just to combine, then add the melted butter and whisk until batter is smooth.
Cover batter with a towel and let it rest at room temperature for 1/2 hour.
Preheat oven with the six cup popover or muffin pan inside until it has reached a temperature of 450 degrees F.
Take the pan out and brush each cup with the remaining melted butter (one Tbsp). Immediately, pour batter into cups filling them two-thirds full.
Return to oven. Bake 15 minutes, then reduce temperature to 375 degrees and bake an additional 20 minutes.
Turn off the oven. Pierce each popover with a paring knife to release steam. Return popovers to the oven and let them stand there for 10 minutes so they can dry inside. Serve immediately.