Preheat the oven: Preheat your oven to 350°F (175°C). Grease a 9×9-inch baking dish or a similar-sized oven-safe dish.

1. Whisk the mixture: In a medium bowl, whisk the eggs until well-beaten. Add the evaporated milk, sweetened condensed milk, whole milk, sugar, and vanilla extract to the eggs. Whisk until the sugar is completely dissolved and the mixture is smooth.
2. Prepare the baking dish: Pour the mixture into the prepared baking dish. Sprinkle the cinnamon over the top (optional) for added flavor.
3. Bake with water bath: Place the baking dish in a larger pan and add hot water to the outer pan, covering about halfway up the sides of the baking dish. This helps cook the leche asada gently and evenly.
4. Bake: Bake for about 45-50 minutes, or until the top is golden brown and a knife inserted into the center comes out clean.
5. Cool and serve: Let the leche asada cool for at least 15 minutes before serving. Refrigerate for a couple of hours to let it set further, if preferred. Slice into squares and serve.