Pour milk into a large measuring cup; whisk until well blended. Place 1 cup milk in a medium pan. Whisk in sugar, espresso, cinnamon, and salt. Sprinkle gelatin over top. Let stand for 5 minutes. Place pan on stove; turn heat to medium and cook, whisking, until mixture is smooth, 1 to 2 minutes.
Stir together kefir, vanilla, and remaining ¾ cup milk in a bowl. Gradually add gelatin mixture, whisking constantly.