Preheat the oven to 350°F. Line an 8-inch springform pan with parchment paper and grease lightly.
Melt butter and chopped bittersweet chocolate in a saucepan over low heat until smooth.
Remove from heat and stir in sugar, salt, and vanilla extract.
Whisk in eggs one at a time until fully combined.
Fold in flour gently and pour the batter into the prepared pan.
Bake for 25-30 minutes until the center is set. Let the cake cool completely.
For the ganache, heat heavy cream in a saucepan until simmering, then pour over chocolate chips in a bowl.
Let sit for 5 minutes, then stir until smooth. Pour ganache over cooled cake and refrigerate until set.