Preheat oven to 180˚F/82˚C.
When the pastila is completely cool, gently peel the parchment paper away. If the pastry sticks to the paper use a spatula to gently scrape it off.
If using quarter-sheet pans cut each layer half for a total of 4 rectangles.
Line a baking sheet with parchment and place one layer of pastila.
Scoop a couple of teaspoons of the reserved batter and with an off-set spatula spread it out evenly. Add another layer of pastila. Repeat for the remaining layers.
Coat the sides and top of the layered pastilla with any remaining batter.
Bake at 180˚F/82˚C for an hour and a half.
Using a dampened knife and a sawing motion, slice the pastila into 1" wide slices.
Gently roll the pastila slices in powdered sugar. Serve with a cup of tea.
Store in an airtight container for a couple of days.