Heat the milk and almond milk in a saucepan over medium heat until almost simmering; remove from the heat. Meanwhile, whisk the cornstarch, salt, sugar and egg in a medium heatproof bowl. Pour about half of the hot milk mixture into the bowl and whisk vigorously until smooth. Pour the mixture back into the saucepan and cook over medium heat, whisking vigorously, until thick and starting to bubble, 1 to 2 minutes. Whisk in the vanilla. Transfer the mixture to a bowl and let cool, stirring occasionally. Cut the bananas into thin slices. Layer a few banana slices, a few pieces of graham cracker and 2 tablespoons of the prepared pudding in each of 4 glasses; sprinkle with cocoa powder and almonds, then repeat to make 2 more layers. Cover with plastic wrap and chill 4 hours or overnight.