Heat a medium size pot of water over low heat to the halfway mark until simmering.
Add the chocolate to a large metal bowl and place directly over the pot to make a double boiler.
Stir the chocolate using a rubber spatula to keep the chocolate moving around to help melt.
Remove the bowl from the double boiler and stir in the butter until completely melted and mixed in.
Next, whisk in 1 egg at a time until mixed in. Set aside.
In a stand mixer add in the egg whites and mix on medium speed until soft peaks are formed, which takes about 3-4 minutes. See note on what to look for.
Slowly pour in the sugar and mix on medium until stiff peaks are formed, which takes about 3-4 minutes.
Remove the egg white mixture (a.k.a. merengue) from the stand mixer and add it to the bowl with the chocolate and gently fold in using a rubber spatula until completely mixed in. Don’t over mix.
Place the bowl in the refrigerator for 90 – 120 minutes or set.
Serve with whipped cream and berries.