In a small saucepan, pour in 1½ cups of milk and add the sugar. Set the pan over low heat and stir gently with a heatproof whisk to dissolve the sugar.

In a small mixing bowl, whisk the remaining ½ cup milk with the cornstarch until completely smooth, with no visible lumps. Slowly pour the cornstarch mixture into the warm milk and sugar in the saucepan, whisking constantly to prevent clumping. Keep the heat low and continue whisking for 5 to 8 minutes, until the mixture thickens to a pudding-like consistency.

Remove the saucepan from the heat and stir in the rose water.

Pour the hot sahlab drink into two heatproof serving glasses or mugs. Garnish with shredded coconut, chopped peanuts, pistachios, or any toppings you like. Serve immediately while hot and thick.