Directions:

Preheat Oven to 300 degrees. Prepare a 9" spring form pan (best)
Spray pan with non-stick baking spray, then line pan with parchment paper (9" round easiest) and spray again. Lay out 2 pieces of foil, criss-cross, and place prepared pan on top. Bring the foil halfway up the pan and press together to seal; this prevents water from getting into the cake during baking. Set the pan into a larger baking dish, roasting pan, or sautee pan (high sides). In a small saucepan, combine water, salt, and sugar. Bring to a simmer and whisk until the sugar is dissolved (can use instant-hot. Melt the chocolate either in a double boiler or in the microwave (time-saver!); if microwaving, melt one minute, (mix) then in 30 sec increments to avoid burning. Pour into the bowl of a stand mixer. Mix on low speed and add in the butter, until incorporated into the chocolate. Add the water-sugar mixture and continue to mix on low speed. Increase speed to medium-low and add the eggs one at a time until incorporated. Pour batter into the 9" prepared pan—into the larger baking dish/roasting pan. pour boiling water into the baking dish/roasting pan approx. halfway up the side (instant hot or microwaved water fine).
Place in the oven and bake for 1 hour, until the cake is set (very firm but not wet).
Remove and let cool to room temp, still in water bath.
Remove pan from water bath, and place in fridge for at least 4 hours (overnight fine)
Remove from pan: unlock pan to remove ring; can place plate as is or remove the pan base by sliding a knife blade horizontally between the cake and pan base and gently shift the cake to a plate.