Figuring how much you need: a class jars has two parts, the main container and the top glass where the screw lid fits. I filled the main container to about 1/2 inch under the glass screw-top band. The following recipe gives you a little more sauce than needed to get to this level so I poured the extra into a second jar and immediately started making another batch of hot fudge. This is easy to do - recipe is fast and simple - so the chocolate will stay warm. I didn't double or triple the recipe, just made batch after batch in the same pan.
Salted Hot Fudge
1/2 cup unsalted butter
2 ounces unsweetened chocolate (chopped a bit)
1/2 cup Dutch process cocoa, sifted
2/3 cup sugar
1 cup heavy cream
1/2 to 3/4 tsp salt (should be very fine if you use sea salt)
2 tsp vanilla
• In a heavy pan melt the chocolate and butter over low heat until melted; stir or whisk
• Add cocoa, sugar and 3/4 of the heavy cream, one at a time. Turn heat up to medium low and stir or whisk constantly for about 3 minutes until sauce is warm and thick (need to whisk constantly so sauce doesn't burn)
• Add the remaining cream and whisk another minute. Sauce will be very smooth.
Cut squares of wrapping paper (Container Store solids are just the right sturdiness) for the lids and use rubber bands (mine are fruit department green from Whole Foods) to hold the paper down. Be creative with tags. I painted cheap packing tie-ons with watercolors, easy enough. Put the jars back in the original carton and all that's left is delivery.