Combine potatoes and both cheeses in a medium saucepan. Heat over low flame, stirring until cheese has melted and is incorporated into the potatoes. (To save time, add the cheeses to freshly made, hot mashed potatoes and they’ll melt right away.)

Season mixture with salt, pepper, paprika, and onion powder. Set aside to cool.

Preheat oven to 400°F (200°C).

Divide puff pastry dough into four even pieces.

Working with one piece at a time, roll out dough to a rectangular shape.

Add one beaten egg to the cooled potatoes and stir to combine.

Spread a quarter of the potato mixture evenly over the dough and roll up lengthwise, jelly-roll style.

Cut into 12 even slices and place on a greased baking sheet.

Repeat with remaining pieces of dough.

Brush with beaten egg and sprinkle with scallions or dried chives. Bake for 20 to 25 minutes, or until golden.