Heat the oven to 325 degrees F. Grease and lightly flour a 9-by-13-inch baking dish.

In a small saucepan, heat the butter and milk over low heat until the butter melts. Remove from heat and set aside.

Whisk the flour, baking powder, salt, and cinnamon in a small bowl and set aside.

In a large bowl, use an electric mixer to beat the eggs on medium speed until smooth and combined. While mixing, slowly pour in the sugar, then increase the speed to medium-high and beat until the mixture is thick and glossy, about 5 to 7 minutes.

Reduce the speed to low and slowly pour in the melted butter mixture and 1 teaspoon vanilla extract. Add the flour mixture in 2 additions, mixing until just incorporated.

Spread the batter evenly in the prepared pan and bake for 30 to 35 minutes until a toothpick inserted in the center of the cake comes out clean. Allow the cake to cool for 10 minutes.

Prepare the milk mixture while the cake bakes: Pour the sweetened condensed milk into a small saucepan and cook over low heat until slightly darker and thicker, about 10 minutes, stirring frequently. Remove from heat and whisk in evaporated milk, 1 cup heavy cream, and 1 ½ teaspoons vanilla extract. Place in the fridge to cool slightly while the cake is baking.

Once the cake has cooled for 10 minutes, use a skewer or chopsticks to poke holes at ½-inch intervals all over the top of the cake. Slowly pour the milk mixture over the cake, taking care to evenly cover the cake. Let it sit at room temperature for 30 minutes, then refrigerate for at least 3 hours or up to 24 hours.

Remove the cake from the fridge 30 minutes prior to serving.

Make the whipped cream topping while the cake rests: Use an electric mixer on medium speed to whisk 1 ½ cups heavy cream, powdered sugar, and 1 ½ teaspoons vanilla extract until soft peaks form. Spread evenly over the cake. Sprinkle with cinnamon and serve.