In a medium bowl, combine eggs, sugar, and salt. Gradually add milk, mixing until thoroughly combined. Then, add vanilla and Grape-Nuts and stir until incorporated.
Pour mixture into an 8×8-inch baking dish. Make a hot water bath by placing the baking dish in a large roasting pan filled with 2-inches of hot water. (You want water to come halfway up the outside of the custard dish.)
Bake for 40-50 minutes, or until a knife inserted in the center comes out clean. Serve plain or with cream