Preheat the oven to 350° F/175° C and set an oven rack in the middle.
In one of the bowls, toss the cherries with the cinnamon and lemon juice. Pour into the prepared baking pan.
In the other bowl, whisk together the flour, ¾ cup sugar, and baking powder. Stir in the milk and melted butter. The batter will be very thick. Spoon over the cherries.
In the same bowl, stir together the remaining sugar and cornstarch and sprinkle over the batter. Slowly pour the boiling water all over the pan. The water will rise up and pool, but it will combine with the batter as it cooks.
Place the foil-covered sheet underneath the cherry pan. Bake in the preheated oven for 55 to 60 minutes, until the cake tests done and is golden and a little crunchy on top. Allow to cool for about 10 to 15 minutes, then serve warm with ice cream.