For the cake: Preheat the oven to 350 degrees F. Butter a 9-by-13-inch baking dish.
Whisk the flour, baking powder and salt in a bowl.
Combine the granulated sugar and eggs in a large bowl and beat with an electric mixer until light and pale, about 3 minutes. Add the flour mixture and mix until just incorporated. Add the melted butter and mix until just incorporated. Pour the batter into the prepared baking dish and even it out with an offset spatula.
Bake until puffed, golden and a wooden pick inserted into the center comes out clean, about 25 minutes. Cool on a wire rack for 10 minutes.
For the glaze: Pour the sweetened condensed milk into a large measuring cup and stir in the cinnamon. Then stir in the evaporated milk, half-and-half and vanilla.
After the cake has cooled for 10 minutes, poke it all over with a wooden skewer and pour the glaze on top. Allow the cake to cool completely, about 1 hour. Cover with plastic wrap and refrigerate at least 4 hours, and preferably overnight.
For finishing: Beat the heavy cream with the confectioners' sugar and vanilla until it just holds stiff peaks. Spoon the cream over the cake and smooth with an offset spatula. Sprinkle with cinnamon. Keep refrigerated until ready to serve.