Place chopped chocolate and vanilla extract in a blender.

In a small pot with a tight-fitting lid, heat water and ginger until just simmering. Turn off heat, cover, and let steep at least 10 minutes. Reheat water and ginger to simmering. Remove from heat and stir in espresso powder until dissolved. Immediately pour over chocolate in the blender, cover, and purée on high until smooth, about 20 seconds. With the motor running, add flax oil. Strain into a large bowl, discarding any ginger bits.

In a separate bowl, whisk egg whites until foamy. Add cream of tartar and continue whisking until stiff but not dry. Fold into chocolate mixture. Pour into eight dessert bowls or goblets. Cover tightly and refrigerate until set, about 3 hours.