Combine the raspberries with sugar and salt; then place in a sealed container in the refrigerator overnight.
The next day, puree the mixture in a mini food processor; then pour through a strainer. You can make this sauce up to 2 days ahead of time and keep refrigerated.
Step 2. Make the Chocolate Espresso Cake
Preheat your oven to 350 degrees F and line the bottom of a 9-inch cake pan with 2-inch high sides with parchment paper. (Note: most home cake pans have 1 1/2-inch sides so if you use this pan, you'll have extra batter.)
In a medium saucepan, bring the butter, espresso and sugar to a boil, stirring until the sugar dissolves. Next add the chocolate and whisk until the mixture is smooth; then remove from the heat and cool slightly (about 5 minutes).
In a separate small bowl, whisk the eggs; then slowly add the eggs into the chocolate mixture until blended. Pour the batter into your prepared pan; then place the pan in a roasting pan. Pour enough hot water into the roasting pan to come halfway up the sides of the cake pan.
Bake until the center of the cake is set and tester inserted into the center comes out with a few moist crumbs; approximately 45-55 minutes. Remove the cake pan from the water and chill cake overnight.
Step 3. Serving the Chocolate Espresso Cake
When you're ready to serve the cake, first take a knife and cut around the pan to loosen it. Put hot water back in the roasting pan and dip the cake pan in the hot water for about 15 seconds. (This will help loosen the cake to help release it from the pan.)
Lift the cake out of the pan, peel off the parchment paper and dust with your cocoa powder or confectioners sugar. Cut the cake into 12 slices and garnish each serving with the fresh raspberry sauce.
*Allow additional time to refrigerate overnight before serving.