Line an 8 inch square pan with parchment paper.
Grease the parchment paper with butter. Set aside.
Combine sugar, corn syrup, half and half, and salt in a heavy saucepan.
Heat over medium low heat, stirring continually, until sugar melts.
Brush down sides with a pastry brush dipped in warm water.
Remove from heat.
Add chocolate and stir until melted.
Return to heat.
Cook to 238℉.
When fudge is close to temperature, sprinkle a marble board with ice cold water.
Remove candy from heat and pour out onto board.
Dot with butter.
Allow to cool to 110℉.
Add vanilla.
Use a bench knife to work the candy, folding it over itself, until it loses its shine, about 10 minutes.
Immediately scoop into prepared pan and spread evenly.
Allow to cool at room temperature for 3-4 hours, or until completely set.
Once set, lift out of pan and cut into desired shapes.