Dark and Chewy Hot Fudge

I really love the hot fudge at old style ice cream shops (or should I say shoppes?). The kind that is gooey and a little chewy once it chills on the ice cream. The only problem is, I usually like my fudge a little darker than the stuff they serve. After searching and testing, this is what I came up with: It has the texture that is more like goo than syrup, with a dark, creamy, taste that's not too sweet and melts in your mouth.

6 oz dark chocolate of your choice
1/4 C cocoa powder (I use a combo of regular and Dutch processed)
2 TBS butter
1 can of sweetened condensed milk
1 tsp Vanilla or coffee extract

Chop chocolate into chunks. Put all ingredients in a saucepan on medium low heat and stir until melted. If you like even chewier hot fudge, cook it for a few minutes after its melted. Use it to make old fashioned ice cream sundaes. Store it in an airtight jar in the fridge. I've never had it go bad on me.