Preheat oven to 375°.

In a large bowl, whisk together eggs and milk. In a separate bowl combine the flour, sugar, salt, and zest. Add to the egg mixture and stir until just combined.

Melt the butter in the microwave and then brush into the cups of a popover pan or muffin pan.The use of baking cups is okay.

Place pan in the oven while the oven finishes preheating, to keep butter warm while you prepare batter.

Pour the batter into the prepared pan, filling each cup to about 2/3 full. Spoon 1 tsp of blackberry fruit spread (or any other flavor) into the center of each cup.

Bake until puffed and golden, about 35 minutes. Serve immediately.