Flour Free Chocolate Cake

I made a flour-free chocolate cake for New Year's eve. It was so delicious that I decided to make it again yesterday but the outcome was not as nice as I have used a different type of chocolate the second time. Here is the recipe:

5 Eggs (I used grade A or Large Eggs)
175 g caster sugar
225 g butter + extra for greasing
200 g plain dark chocolate
75 g ground almonds, sieved

1. Preheat oven to 180 C (350 F). Grease the baking tin and place in the fridge.
2. Beat the eggs in a large bowl, just enough to break the yolks, then add the sugar. Combine the mixture with a whisk, stopping as soon as it is evenly blended.
3. Put the butter and the chocolate in a saucepan over a medium heat. When the butter has melted, turn off the heat and stir with a flexible spatula until the chocolate has also melted.
4. Pour the chocolate over the eggs and very lightly mix with the whisk. Add the ground almonds and mix again.
5. Pour the mixture into the tin, and give it a tap on the work surface to release any air bubbles. Transfer to the oven for 25 minutes maximum.

**For the first time I used normal cooking chocolate bought from baking supplies store and it came out beautifully. For the second time I used non-sweeted cooking chocolates and the result was not as nice as the cake tasted like dark chocolate with a hinge of bitterness. Happy baking.