Heat the oven to 350 degrees and grease a 9-inch pie dish.
Put the blueberries, ¼ cup/50 grams sugar and the lemon zest and juice in a small saucepan. Bring to a simmer over low heat, stirring here and there for 3 to 5 minutes, or until the sugar has dissolved and the berries are glossy. Turn off the heat and set aside.
In a medium bowl, cream the butter and remaining ½ cup/100 grams sugar together until the mixture is pale and fluffy. Add the egg and stir to incorporate fully before adding the sour cream. Stir to combine and set aside.
In another medium bowl, combine the cornmeal, almond meal, baking powder and salt, and whisk. Make a well in the center and pour in the wet ingredients. Whisk to form a smooth batter, then pour into the greased pie dish, leveling the batter with a spatula or the back of a spoon.
Spoon over the blueberries with their juices somewhat evenly distributing them and leaving some batter uncovered. Sprinkle with sugar to evenly cover the surface. Set the pie plate on a baking sheet to catch drips.
Bake for 45 to 55 minutes, or until the cake has taken on a deep nutty color around its edge, and a blueberry-less area of sponge springs back when you press with a finger. The jammy areas will feel underbaked and that is good.
Leave to cool a little before serving warm with sour cream or vanilla ice cream, or both.
