To make the crust: Put oven rack in middle position and preheat oven to 325 degrees F. Line bottom and sides of an 8-inch square baking pan with 2 sheets of foil (crisscrossed), leaving a 2-inch overhang on all sides.
Finely grind crackers with sugar and a pinch of salt in a food processor. With motor running, add butter, blending until combined. Press mixture evenly onto bottom of baking pan. Bake 10 minutes, then cool in pan on a rack 5 minutes.
To make the filling: Sprinkle gelatin over milk in a small bowl and let stand 2 minutes to soften.
Beat together cream cheese, eggs, salt, and gelatin mixture in a bowl with an electric mixer at medium speed until well combined, about 2 minutes, then stir in the dulce de leche gently but thoroughly. Pour filling over crust, smoothing top, then bake in a hot water bath in oven until center is just set, about 45 minutes. Cool cheesecake completely in pan on rack, about 2 hours. Chill, covered, at least 6 hours.
Glaze cake within 2 hours of serving. Heat all glaze ingredients in a double boiler or a small metal bowl set over a saucepan of barely simmering water, stirring until smooth, then pour over cheesecake, tilting baking pan to coat top evenly. Chill, uncovered, 30 minutes.
Lift cheesecake from pan using foil overhang and cut into 1-inch squares with a thin knife, wiping off knife after each cut.