Note from papa Terry: "this is the best chocolate dessert I've ever had!"
Preheat oven 400°.
Butter and flour 8" spring form pan. Line bottom w/baking parchment or wax paper. In a double boiler over hot (but not!) simmering water, put 1/2 choc and 1/2 butter. Stir and melt, add the balance of choc and butter gradually, stir and melt.
Remove and let stand until tepid. Whisk eggs and sugar until frothing in a heat proof bowl.
Set the bowl in a ban of hot (but not!) simmering water (should touch the bottom of the bowl). Continue whisking until mixture is warm to touch. Remove from heat.
Beat the egg mixture at med-high speed 4-5 min until it triples in volume and soft peaks form.
Sift flour over the egg mixture and gently fold in. Fold in 1/4 of the egg mix into the chocolate to lighten it. Carefully fold in the lightened chocolate mixture into the egg mix. Scrape into prepared pan.
Bake 15-20 min or until a cake testr comes out slightly moist.
Cool 45 min or until completely cool. Remove pan sides, invert on a plate and remove bottom + wax paper and re-invert onto another plate.
Serve with creme anglaise or whipped cream or ice cream or raspberry puree.