For the fudge sauce: Combine the semisweet chocolate, heavy cream, light corn syrup, sugar and cocoa powder in a small saucepan over medium heat. Cook, stirring constantly, until the chocolate is melted.
Take the pan off the heat, and add the unsalted butter and vanilla extract. Continue to stir the fudge sauce until completely smooth.
Cool the sauce slightly before serving.
For the caramel sauce: Combine the sugar, light corn syrup and 1/2 cup water in a medium saucepan over medium-high heat. Cook, stirring constantly, until the sugar dissolves.
Bring the mixture to a boil. Once boiling, swirl the pan occasionally, but do not stir, until the caramel turns a deep-amber color, 10 to 12 minutes.
Reduce the heat to low, carefully add the heavy cream, stir to incorporate and simmer until smooth.
Remove the pan from the heat, stir in the butter and pinch of salt and cool the caramel sauce slightly before serving.
For the sundae bar: Serve the ice cream with the fudge sauce, caramel sauce, and sundae toppings.