Preheat the oven to 325°F. Grease and line the bottom of a 9-inch springform pan with a round of parchment paper. Grease the sides of the pan as well.
Melt the chocolate and butter in a large heat-proof bowl over a saucepan with simmering water. Stir occasionally. Remove from heat and set aside.
In a large bowl, at medium speed, beat eggs, sugar, vanilla, espresso powder, and salt until doubled in size.
Fold 1/3 of the egg mixture into the chocolate mixture until just incorporated. Repeat the process two more times.
Wrap the springform pan with aluminum foil and place in a large roasting pan. Pour the batter into the prepared pan and smooth the surface with an offset spatula. Place the roasting pan in the oven and add hot water to come up 1-inch of the spring form pan. Bake for 40-45 minutes or until the center is set. Do not overbake. Remove from oven and allow the cake to cool down to room temperature. Refrigerate for at least 6 hours or overnight. Run a sharp knife around the sides of pan. Remove from pan. Dust with cocoa powder and decorate with fresh raspberries and thyme sprigs. Serve
Serve the cake with sweetened whipped cream or ice cream.