Prepare a querter sheet an, by lightly coating with pan spray and placing a parchment on top. Be sure to spray the top of the parchment paper as well. Place the sheet pan inside a half sheet pan and set aside.
Next, bring the water and sugar to a boil over medium heat, stirring until the sugar is just disssolved.
Simmer the simple syrup for 5 minutes and then remove from the heat.
Melt the butter in a saucepan over low heat. Add the chocolate and whisk until smooth.
The whisk the simple syrup into the chocolate and cool slightly.
Add the whole eggs to the chocolate mixture and whisk until well blended.
Pour the batter into the prepared quarter sheet pan. Next, filll the half sheet pan with hot water, halfway up the querter sheet pan.
Place in the oven and bake for 20 - 40 minutes, until just set on top.
Allow the cake to cool for 10-15 minutes after it has been taken out of the oven, then remove from the sheet pan and cut to desired size.