For the Ice Cream
Set a fine-mesh strainer over a large heatproof bowl and set aside.
Combine the cream, milk, and vanilla bean seeds in a large saucepan and bring to a simmer over medium heat. Remove from heat and whisk in cocoa powder. Add the 10 ounces of chopped chocolate morsels and let it sit for a couple of minutes while they soften. Whisk until the mixture is completely smooth and set aside to cool.
In a stand mixer (or with a hand mixer), beat the egg yolks until they are smooth. Slowly add the sugar and whisk until it is smooth and the mixture is pale yellow. With the beater running, slowly pour 1 cup or ladle of the chocolate mixture into the eggs. Then repeat with a second cup. Work slowly so the hot mixture doesn’t scramble the eggs.
Then pour the chocolate-egg mixture back into the saucepan with the rest of the chocolate. Cook over low heat, stirring constantly, until the mixture thickens and will coat a spoon, about 5 minutes.
Remove from the heat and strain the mixture through the prepared fine-mesh strainer. Stir in the vanilla extract and salt, and then put the bowl in the fridge about 15 to 20 minutes to cool. Cover with plastic wrap and put back into in the refrigerator for at least a few hours or overnight. You can do this step a couple of days in advance as long as you keep it covered in the fridge.
When the mix is cold, put it in an ice cream machine and prepare according to the manufacturer’s instructions. When the ice cream is almost done, add the extra 1 cup of dark chocolate morsels. Then stream in the caramel and fudge sauce immediately before turning the machine off.
For the Dark Chocolate Base
On a stove top using a double boiler and medium-low heat (or a heat-proof glass bowl over a small sauce pan with simmering water), melt the chocolate, stirring fairly constantly. Stir in the vanilla extract, then add the pretzel pieces and mix until they are fully coated.
For the Salted Caramel Sauce
Put the heavy cream into the microwave for about a minute to warm it up.
Spread the sugar out in a medium frying pan and put over medium heat. Let it sit until the sugar starts to liquefy and then stir slowly until it is all liquid and an amber color. Take off the heat and carefully add the heavy cream into the sugar, stirring constantly, until combined. If it seizes up (the sugar gets hard), cook over a low heat until the sugar all melts. Add in the vanilla extract and salt. This can be made in advance as long as it is kept in an air-tight container in the fridge.
For the Fudge Sauce
Over medium heat, melt the butter into the cream. Then whisk in the sugar until it is dissolved. Lower the heat and add the chocolate chips in and let it sit for about 2 minutes (until the chips are soft) and then stir them into the cream. Mix in the vanilla extract and salt, and remove from the heat to cool. This can be made in advance as long as it is kept in an air-tight container in the fridge.
To Assemble the Cake
Line a 9” spring form pan with plastic saran wrap. Put the frozen ice cream into the prepared spring form pan and freeze until hard. Then prepare the dark chocolate pretzel base and spread evenly over the top of the ice cream layer and freeze for at least 6 hours or overnight. When you are ready to serve, unlock the spring form pan and remove the sides. Then flip the cake over – quickly and carefully! – so that the chocolate base is on the bottom. Remove the plastic wrap. Slice and serve frozen with whipped cream, crushed pretzels, and leftover caramel and fudge sauce drizzled on top.