Preheat the oven to 350°F (175°C). Grease an 8-inch springform pan thoroughly with cooking spray or butter.
In a microwave-safe bowl, melt the butter for 1–2 minutes until fully melted.
Add the 8 ounces semisweet chocolate to the melted butter and microwave an additional 30 seconds, then let sit 3–4 minutes before stirring until smooth.
Stir in the sugar until blended and allow the mixture to cool slightly.
When the chocolate mixture has cooled enough not to cook the eggs, stir in the well-beaten eggs until fully combined, then pour the batter into the prepared pan.
Bake for 30–35 minutes, or until a thin crust forms on top and the center is just set. Remove from oven and cool to room temperature, then refrigerate overnight in the pan.
When ready to ice, remove the cake from the pan and place it on a wire rack set over a baking sheet to catch drips.
Heat the 1 cup heavy whipping cream in a saucepan until it is just about to boil, then remove from heat. Add the 10 ounces semisweet chocolate chips and let sit 4–5 minutes.
Stir the cream and chocolate until smooth to make a glossy ganache, then pour the ganache over the cooled cake and spread it over the top and sides.
Carefully transfer the iced cake to a serving plate and serve each slice with a dollop of whipped cream or a scoop of vanilla ice cream, if desired.