In a large bowl, whisk together the large eggs and milk. In a separate bowl combine the flour, sugar, salt, and zest. Add to the egg mixture and stir until just combined. It's okay if it's a little lumpy.
Melt the butter in the microwave and then brush it into the cups of a popover pan or muffin pan. Place pan in the oven to heat it up while the oven finishes preheating.
Pour the batter into the prepared pan, filling each cup to about ⅔ full. Scatter a few raspberries over the tops of each cup. Bake until puffed and golden, about 35-45 minutes. Serve immediately, popovers will deflate slightly as they cool.
Note: If you don't have a popover pan, a muffin pan will work just fine.