Make the orgeat: Preheat the oven to 325°. Place the almonds on a baking sheet and toast for 10 minutes. Remove the nuts and set aside to cool to room temperature. In a food processor, grind the nuts until they are very finely ground.
In a medium saucepan set over medium heat, combine 1 cup water and the sugar. Stir until the sugar is dissolved, then stir in the ground almonds. Set aside to cool, then strain through a fine-mesh strainer and discard the almonds. The syrup can be kept, refrigerated, for up to 3 weeks.
Make the cocktail: Fill a cocktail shaker with ice cubes and add the rum, Curaçao, orgeat syrup, Demerara syrup and bitters. Cover and shake well, then strain into a tiki glass mug. Pack the mug with crushed ice and garnish with the lime wedge, an umbrella and a straw.