Preheat the oven to 350 degrees F (or 175 degrees C). Prepare your cake pan. I used my French cake pan 4" x 8". Line with parchment for easy removal, cut to size so you have enough tumbling over the edges of the pan to pull the cake out carefully.
Mix the butter, eggs and sugar until slightly frothy and foamy with a hand mixer or stand mixer.
In a separate bowl, mix the dry ingredients with the chocolate. So the flour, baking powder, and salt.
Then mix the dry ingredients into the wet ingredients until fully combined.
Pour into your cake pan (again, if the butter wasn't fully liquid, your batter will be a bit thicker and that is okay!).
Before placing into the oven, sprinkle the muscovado over the top, generously as this will add wonderful texture to the top of the cake.
Depending upon the size of your pan. If narrower and shorter (like mine), bake for about 35-40 minutes. If the batter is able to spread out a bit more, bake for 25-30 minutes. Simply test with a clean knife to make sure the cake is baked through (but not over baked).
Remove and let sit for about 10 minutes to cool, and then remove gently, slice and enjoy!