- Preheat oven to 300F, with rack on lower middle position. Pour boiling water into a large baking pan, and place pan in oven on lowest rack.
- Line a 8 1/2 inch springform pan with parchment on bottom. Grease and flour (any gluten-free flour would work) the parchment and sides of springform pan. Wrap the exterior of pan with heavy duty foil.
- In a small saucepan, combine the prepared coffee and sugar. Stir over medium heat until sugar is comletely dissolved. Set aside.
- In a heavy pan (I use my All-Clad), on lowest heat, stir the bittersweet chocolate chunks until just small bits of chocolate remain unmelted. Turn heat off, remove pan from heat, and continue stirring to finish the melting until chocolate is completely smooth.
- Transfer melted chocolate into bowl of stand mixer. Slowly beat the butter into the chocolate, 1 piece at a time. Gently beat in the hot coffee/sugar mixture.
- Beat in the eggs, one at a time, just until fully combined. Scrape the bowl and ensure that all batter is fully smooth and incorporated.
- Pour batter into prepared springform pan. Bake for 45 minutes on lower middle rack. The center should be wet-looking, with edges looking done and puffy. The cake will set as it cools, so don’t worry about the jiggly center.
- Let cake cool to room temp in springform pan, and then cover/chill overnight in fridge. To unmold, run a thin plastic knife carefully between cake and pan all around the edges. Unlock springform, and it should release cake easily. Keep chilled until ready to serve. Slice chilled cake and serve with berries and whipped cream, if desired.
NOTES
Be sure to allow cake to chill in fridge overnight, to allow it to set firmly. Must serve it chilled, especially if room is warm. Leftover cake freezes nicely. Wrap up airtight and freeze for several weeks.