Preheat oven to 300°F (150°C).
In a large mixing bowl, beat the mascarpone with an electric mixer for about 2–3 minutes until smooth and creamy.
Melt the chocolate using a double boiler or microwave in 30-second intervals, stirring between each interval until fully melted and smooth.
Pour the melted chocolate into the mascarpone and beat until fully combined.
Add the eggs one at a time, mixing well after each addition. Add the powdered sugar and mix again until smooth.
Add the flour and gently fold it in using a spatula. Stop mixing as soon as the flour is fully incorporated. Do not overmix.
Pour the batter into a greased 8- to 9-inch round pan (silicone pan works especially well).
Bake for approximately 20 minutes. Allow the cake to cool completely, then refrigerate for 2 to 3 hours.