Make the syrup: Bring the water, sugar, and lemon to a boil and cook for 5 minutes.
Prepare the cornstarch slurry: Whisk the water and cornstarch together until completely smooth and lump-free.
Combine: Slowly add the cornstarch mixture to the boiling syrup, whisking constantly.
Stir the lemon juice into the mixture.
Cook the Candy Carefully: Cook the mixture over medium-low heat, whisking constantly, until it becomes thick, glossy, and pale yellow. The finished mixture should be elastic and pliable rather than runny.
Pour: Transfer the hot mixture onto a lightly oiled work surface.
Spread: Working quickly, spread the mixture to about ¼-inch thickness.
Cut: Dust the surface with powdered sugar and cut into 2-inch rounds, about ¼ inch thick.
Prepare the ashta: Place the clotted cream in a fine-mesh sieve and let the excess liquid drain before using.
Fill the Malban as close to serving as possible. The moisture in the ashta can soften the candy over time and make it difficult to handle.
Dust the surface generously with powdered sugar. Cut the Malban into 2-inch rounds using a lightly dusted cutter.
Serve: Garnish with finely ground pistachios and serve with Turkish or Arabic coffee.
Storage: Because Malban Bel Ashta is filled with fresh clotted cream, it is best enjoyed the day it is assembled. Refrigerate any leftovers in an airtight container and bring them to room temperature briefly before serving.