Review: A flourless, low-carb brownies

I tried a low-carb brownie recipe where the goodies are baked on a muffin pan. The recipe I used was as follows:

Ingredients:

1/4 cup butter
3 Tbsp cocoa powder
1 egg
2 Tbsp water
4 packets (4g) NutraSweet
1 tsp white granulated sugar
1/4 tsp vanilla

Procedures:

Preheat oven to 175 degrees Celsius. Line muffin pan with muffin liners.
Melt butter then mix in the cocoa powder
Add the egg, water, vanilla, and NutraSweet. Mix well.
Fill each muffin liner 2/3 full. Bake for 15 minutes.

The recipe gave me 3 cups of brownies.

The result:

The taste? Bitter. Needs more sweetness. Like what others say, I think aspartame in NutraSweet becomes less sweet when heated. Maybe I should use a different sweetener for baked goods.

Some of the other sweeteners I can get are Maltitol syrup and Isomalt.