Start the chestnut puree. Preheat the oven to 400 degrees F. On the flat sides of your chestnuts, create an "X" though the shells. Place on a baking sheet and roast for 15 - 20 minutes. Allow to cool, then remove the shells from the chestnuts.

In a saucepan, add the sugar and water and bring to a boil. Add the chestnuts and cook until the liquid is halfway gone. Add in the vanilla and salt. Remove the chestnuts and reserve the liquid. Puree the chestnuts in a food processor or blender, then slowly add the reserved liquid until the chestnuts are a smooth, creamy paste. If you find you need more liquid, you can add water one tablespoon at a time.

Allow to cool completely.

In a clean and chilled mixer, add the whipped cream and beat until soft peaks form. Whip in the coffee.

Take ⅔ of the chestnut puree (you won't need the remaining puree, save it for adding to your hot chocolate or use as a spread on toast!) and gently fold the whipped cream into the puree. Set aside in the refrigerator.

Make the pate a choux. Preheat the oven to 425 degrees F. Place parchment on two baking sheets. Add the water, milk, and butter into a saucepan and heat until the butter is melted and the liquid is hot and steaming, but not boiling. Take off from the heat and add the sugar, salt, and flour. Mix until well combined.

Add in the eggs one at a time, beating until each egg is fulling incorporated before adding the next.

Fit a piping bag with a large plain round tip and fill with the pate a choux. Pipe 5-inch lengths on the parchment paper, leaving 2 inches of space between them. You can also pipe large rounds about the size of golf balls for profiteroles. Use a moistened finger to pat down any point where you piped the dough.

Bake for 15 minutes, then crack the oven open (I used a wooden spoon to pry open my oven door) for 25 minutes.

Remove and transfer to a wire rack. Cut open lengthwise, or use the back of a wooden spoon to spear through the eclairs.

Make the ganache. Heat the chocolate and heavy cream together in a double boiler, or in a microwave at 50% power for 30 second intervals, mixing between each interval. Mix until the chocolate and heavy cream are completely combined.

Fill a piping bag with the chestnut cream filling and fill the eclairs and/or profiteroles.

Top with the ganache and serve immediately. May store in an air tight container for up to 5 days.