Cut the frozen cherries in half (it’s easiest to do this while they’re frozen). Put them in a bowl and stir in 1 teaspoon sugar and rum extract, if using. Allow them to sit at room temperature until they’ve completely thawed and become juicy, 1-2 hours.
Oil or pan spray 4 7-ounce ramekins. Preheat the oven to 350F. Mix together the brown sugar and 2 tablespoons cocoa powder and set aside.
Pour the juices off the cherries into a measuring cup. Press lightly on the cherries to get all of the juice (I had about 1/4 cup). Sprinkle the corn starch over the cherries and mix well. Divide the cherries equally among the 4 ramekins.
In a medium bowl, combine the flour, salt, 1/3 cup sugar, 1 1/2 tablespoons cocoa, and baking powder. Stir in the vanilla extract, soy yogurt, and soymilk. (Mixture will be very thick.) Drop by tablespoons over the cherries in the ramekins, dividing equally among them. Smooth to cover the cherries.
Sprinkle the brown sugar mixture evenly over the batter, about 2 tablespoons per ramekin. Use a spoon to level the tops.
Add boiling water to the cherry juice up to the 3/4 cup line. Pour or spoon it gently over the brown sugar in the ramekins, about 3 tablespoons per ramekin. Place the ramekins in the oven and bake for about 25-30 minutes, until tops appear mostly dry (they should be streaked with darker, wetter looking areas) and sauce is bubbling around the edges. Remove from oven and allow to cool for 15 minutes before serving.