Step 1

FOR THE BLUE CHEESE BUTTER: Whip butter with fork until light and fluffy. Mix in blue cheese and chives and season with salt and pepper to taste. Cover with plastic wrap and let rest to blend flavors, about 10 minutes, or roll into log and refrigerate. (Leftover butter can be refrigerated in an airtight container for up to 4 days or frozen for up to 2 months.)

Step 2

FOR THE POPOVERS: Adjust oven rack to middle position and heat oven to 400 degrees. Lightly spray cups of popover pan with vegetable oil spray. Using paper towel, wipe out cups, leaving thin film of oil on bottom and sides.

Step 3

Whisk together flour, chives, dry mustard, salt, and cayenne in 8-cup liquid measuring cup or medium bowl. Add milk and eggs and whisk until mostly smooth (some small lumps are OK). Whisk in blue cheese. Distribute batter evenly among prepared cups in popover pan. Bake until popovers are lofty and deep golden brown all over, 40 to 45 minutes. Serve hot, passing blue cheese butter alongside. (Leftover popovers can be stored in zipper-lock bag at room temperature for up to 2 days; reheat directly on middle rack of 300-degree oven for 5 minutes.)