1. Preheat oven to 350 degrees F. Prepare 9 inch springform pan by buttering bottom.
2. Chop butter and chocolate and place in glass mixing bowl set over a pan of simmering water. Stir until melted.
3. Beat eggs until fluffy. Fold in flour. Fold vanilla, kosher salt and butter/chocolate mix. Pour into prepared pan,
4. Bake 25 minutes.
5. Cool on rack.
The cake will rise fairly high while baking and upon cooling will decompress until it is about 1-1/2 inches high. This is normal.