1. Preheat the oven to 350℉. Spray a 9x13-inch baking dish with cooking spray, or brush it with softened butter. Set the baking dish aside.
2. In a small mixing bowl, beat together the 5 egg yolks with ¾ cup of sugar on High using a handheld mixer or the whisk attachment on a stand mixer. After 1-2 minutes, the color will be a pale yellow and the texture will be smooth and ribbony. Add the vanilla extract and ½ cup of whole milk, and beat on low until just combined.
3. In a large mixing bowl, whisk together the flour, baking powder, salt, and chai spice. Pour the egg yolk mixture into the bowl and mix until it's a smooth batter with no lumps.
4. In a large mixing bowl, beat the egg whites on high on High using a handheld mixer or the whisk attachment on a stand mixer. Once the eggs become frothy, slowly start to add in the ¼ cup of sugar in intervals while continuing to mix. Keep going until the meringue forms stiff peaks.
5. Add a ⅓ of the fluffy egg whites into the bowl of cake batter. With a rubber spatula, gently fold in the egg whites until fully combined. Keep doing this with the rest of the egg whites in thirds. Be sure to scrape the sides and bottom of the bowl and keep going until everything is combined with no white streaks.
6. Transfer the cake batter into the greased baking dish. Pop the baking dish into the oven for 35-40 minutes. Insert a toothpick into the center. The cake is done if it comes out clean. Allow the cake to cool for half an hour.
7. While the cake cools, prepare the masala chai tres leches. In a saucepan, bring the evaporated milk and ¼ cup of whole milk to a boil. Add a tablespoon of chai spice and a tablespoon (or 4-5 teabags) of black tea leaves. Simmer for 5 minutes, then turn off the heat. Stir in the condensed milk until it has melted into the mixture.
8. Let the masala chai tres leches mixture fully cool. Then strain it into a liquid cup measurer with a fine mesh strainer. There should be about 2 cups of liquid.
9. Once the tres leches and cake has cooled, poke holes into the cake with a fork, being sure to reach all the way to the bottom. Slowly pour the tres leches mixture all over the cake and the sides. Cover the cake and refrigerate for up to 3 hours.
10. While the cake is chilling, soak Medjool dates in warm to hot water for 10 minutes until soft and plump. Transfer the date into a food processor and pulse until they become a paste. Add ¼ teaspoon of salt and a tablespoon of chai spice into the food processor.
11. Run the food processor on High while slowly pouring in 6 ounces of coconut milk. It's done when it's completely smooth and thick.
12. 30 minutes before serving, beat heavy cream in a large mixing bowl just until soft peaks start to form. Add ½ - 1 cup of the chai date caramel, depending on sweetness preference, and beat until fully mixed and soft peaks have formed.
13. Plop the chai date caramel whipped cream onto the cake and fully spread it out using an offset spatula.
14. To serve, add a few extra dollops of chai date caramel in random areas and spread it into the whipped cream. Garnish with chopped pistachios or sliced almonds. Cut the cake into slices and serve on cake plates.
*While Medjool dates are high in natural sugars, they are low on the glycemic index thanks to a balanced amount of soluble fiber. The complex carbohydrates found in Medjool dates are digested at a slower rate, making them a source of dietary fiber and releasing energy to the body over a longer period of time.