Line an 8-inch square pan with parchment paper and grease thoroughly.
In microwave-proof bowl, melt chocolate and sweetened condensed milk in microwave on high for 1 minute.
Remove from microwave, stir, then heat for another minute. Remove from microwave and let sit for 3 minutes.
Stir melted chocolate vigorously. If not fully melted, place back in microwave for 15 seconds. Stir until mixture is completely melted and smooth.
Add maple syrup and salt slowly until combined and thick.
Pour mixture into pan and add toppings (if using).
Let sit at room temperature for at least 3 hours before serving.