• Preheat oven to 350F.

crust

• If making your own crumbs, grind the chocolate cookies or wafers in a food processor and measure out 1 1/2 cups. Combine with the melted butter until everything is evenly moistened and the mixture feels like wet sand.
• Press the crust into a 10-inch tart pan with a removeable bottom, and up the sides, making sure it is well packed in and even. Using the bottom of a flat measuring cup helps.
• Bake the crust for 10-12 minutes. Set side to cool.

tart

• To make the ganache, heat the heavy cream in a saucepan until it is just starting to simmer. Don't let it get too hot, remove when you see those first tiny bubbles.
• Remove from the heat and add the chopped chocolate, and let sit for a few minutes. (Exactly how long will depend on how big your chocolate pieces are. The smaller the pieces, the more quickly they will melt. You want to err on the side of not letting the cream cool down too much so that the ganache is still warm and will pour smoothly.)
• Whisk the ganache mixture until it is smooth and shiny. Add the butter, a couple pieces at a time, whisking well.
• Pour the ganache into the prepared tart shell. Carefully place the tart in the refrigerator to set for at least 2 hours before slicing. Scatter the sea salt over the top of the tart when it has set so that it doesn't sink in to the chocolate.
• Tip: if you're worried about your knife sticking to the fudgey chocolate filling while slicing, running your knife under hot water and wiping it clean just before slicing will help get a nice clean slice.
• To make the whipped cream, whip the cream, vanilla paste, salt and sugar together until it forms soft peaks.