Combine first 3 ingredients in a medium bowl, stirring with a whisk until blended.
Let stand 30 minutes.
Preheat oven to 37
Weigh or lightly spoon flours into dry measuring cups; level with a knife.
Combine flours and salt, stirring with a whisk. Gradually add flour mixture to milk mixture, stirring well with a whisk. Stir in parsley, rind, and garlic.
Coat 6 popover cups with cooking spray; brush butter evenly among cups to coat.
Place popover cups in a 375 oven for 5 minutes. Divide batter evenly among prepared popover cups.