Preheat the oven to 300°F (149°C). Crack the eggs into a quart container, or medium-sized mixing bowl. Add the salt, heavy cream, and milk, then use an immersion blender, or whisk, to beat the mixture until homogeneous.
Lightly grease an 8x8” (20x20 cm) baking dish with cooking spray. Transfer the beaten eggs into the pan, optionally passing them through a fine mesh strainer for a smoother consistency.
Place the 8x8” pan inside a 9x13” (23x33 cm) baking dish. Carefully pour boiling water into the 9x13” pan so that it reaches about halfway up the sides of the 8x8” pan. Tent the entire setup loosely, then transfer to the preheated oven. Bake for 25-30 minutes, or until fully set. Let cool slightly then flip onto a cutting board and slice into four 4x4” (10x10 cm) squares.
