Preheat oven to 400

Generously butter a 9 inch round cake pan with 2 inch sides and dust with flour

Melt butter and chocolate in a heavy sauce pan over very low heat

Remove from heat and whisk in sugar and eggs, one by one

Stir vigorously for 2-3 minutes then gently whisk in flour and salt

Pour into pan and rap on counter to flatten

Bake for about 20 minutes

Run knife along edge of pan

Allow to cool for 10 minutes before unmolding and allowing to cool completely on rack