1. Make the crust first: in the bowl of a stand mixer, beat the butter on medium speed until light and fluffy, about two minutes. Add the sugar and beat until thoroughly mixed
2. Using a fork or a small whisk, mix the flour salt, and vanilla paste in a small bowl. Add to the butter mixture in two batches, mixing thoroughly after each addition. Remove the dough from the bowl and shape into a disk.
3. Heat oven to 350˚.
4. The dough is ready to use. Press into 9-inch tart pan
5. Place tart shell on a baking sheet and bake for 20-25m minutes, until the edges have a hint of golden color. Transfer the tart pan to a cooling rack and cool completely.
6. Make the ganache: Pour the champagne, cognac, and vanilla into a measuring cup.
7. Combine the melted chocolate in a medium bowl. Pour the cream over the chocolate and using a small silicone spatula, stir the mixture in one direction, concentrating on the center, until the ganache is smooth and glistening.
8. SLowly pour the champagne into the ganache, whisking constantly. Add the butter and stir until it is completely melted, about one minute. Put the ganache in the coolest part of your kitchen and let it set, stirring occasionally until spreadable, about 1 hour.
9. Spread into tart shell, and let set in fridge. Slice and serve.