Blend the corn. Add the 1 1/2 cups fresh corn kernels, 1/2 cup of whole milk, and 1/2 cup water to a blender. Blend for 1 to 2 minutes, until the corn is as smooth as possible.
Strain the mixture. Set a fine-mesh strainer over a large saucepan. Pour in the blended corn and press firmly on the solids with the back of a spoon to extract as much liquid as possible. Discard the pulp.
Simmer. Add the remaining 1 cup whole milk, 1 cinnamon stick (canela), 3 tablespoons brown sugar, and pinch of kosher salt to the strained corn mixture. Warm over medium heat, stirring frequently with a wooden spoon, until it reaches a gentle simmer, about 4–5 minutes. Don't let it boil vigorously.
Make the cornstarch mixture. In a small bowl, whisk together 2 teaspoons cornstarch and the additional 2 tablespoons cold whole milk until smooth and free of lumps.
Thicken the atole. Reduce the heat to medium-low. Slowly pour the cornstarch mixture into the saucepan while stirring constantly. Cook for 3–4 minutes, stirring frequently, until the atole reaches a creamy consistency and lightly coats the back of a spoon.
Finish with vanilla. Remove the saucepan from the heat and discard the cinnamon stick. Stir in 1 teaspoon vanilla extract. For an extra-silky texture, strain the atole once more through a fine-mesh strainer.
Serve warm. Pour the atole into mugs and finish each with a sprinkle of ground cinnamon. Serve immediately.
