Spray 6 half-cup heatproof custard cups or ramekins with cooking spray. Place cups on a rimmed baking sheet.
In a saucepan, whisk together Splenda Sweetener and cornstarch. Add coconut milk and whisk until mixture is smooth. Slowly add half-and-half or milk, whisking constantly to prevent lumps.
Add eggs and salt; whisk until smooth. Cook over medium heat, whisking constantly, for 6–8 minutes or until mixture bubbles and thickens.
Remove saucepan from heat, continuing to whisk rapidly to cool the mixture. Stir in coconut extract.
Transfer custard to prepared dishes; smooth tops. Cover with plastic and refrigerate for at least 4 hours.
To serve, preheat broiler. Sprinkle brown sugar evenly over tops of chilled custards. Broil 6 inches from heat source for 3–5 minutes, or until sugar is caramelized. Watch carefully so the sugar doesn’t burn.