Preheat the oven at 350F or 180C.
In a bowl, sieve the flour, cocoa powder, baking powder and soda together. Then add the sweetener and salt. Mix until well combined.
Add all the wet ingredients and whisk until well combined. The batter is smooth and moderately thick.
In the video, I used a 9x13 inch pan lined with parchment paper. You can also use any suitable pan. Transfer the batter into the pan and spread evenly.
Bake at the middle rack for about 15 to 20 minutes or until a toothpick comes out clean
Meanwhile, make the frosting.
Add all the ingredients into a bowl (except the pecans). Add 2 to 3 tbsp of hot water first. Then whisk to combine. If the cream is too thick, add another tbsp of hot water until you get the right consistency. I added a total of 4 tbsp to get the consistency I wanted. It could be different for you. They key is to add more or less hot water to adjust the thickness of the cream.
Add the roasted chopped pecans and mix with a spatula to combine.
You can frost the cake while still warm or at room temperature.
Pour the cream onto the top of the cake and spread evenly. As my cake was still warm, I chilled it in the fridge for about 30 minutes until the frosting is set enough. The longer you chill the cake, the firmer the frosting will become.
The cake can be kept in the fridge for up to a week.