How to Make It
Preheat the oven to 300°. Butter a 9-inch square cake pan. In a medium bowl, whisk the flour with the baking powder. In another medium bowl, using a handheld electric mixer, beat the egg whites at medium-high speed until soft peaks form. In a large bowl, beat the egg yolks with the sugar at medium-high speed until pale and thickened, about 3 minutes. At low speed, beat in the whole milk, then beat in the flour mixture. Using a rubber spatula, fold in the beaten egg whites until no white streaks remain.
Scrape the batter into the prepared pan and bake in the center of the oven for about 45 minutes, until the top is golden and a toothpick inserted in the center comes out clean. Transfer the pan to a rack and let the cake cool completely, about 2 hours.
Using a fork, poke holes all over the cooled cake. In a large bowl, whisk the condensed milk with the evaporated milk, heavy cream and vanilla. Spoon the milk mixture all over the top of the cake, allowing the cake to absorb it before adding more. Let the cake stand for 30 minutes.
In a small saucepan, combine the sugar with 1/4 cup of water and simmer over moderate heat, without stirring, until the syrup reaches 238° on a candy thermometer, about 10 minutes. In a standing mixer fitted with the whisk, beat the egg whites with the cream of tartar at medium speed until foamy. Continue to beat until soft peaks form. Gradually drizzle in the hot syrup and beat at high speed until the meringue just holds stiff, glossy peaks. Beat in the vanilla.
Pour off any excess milk from the cake. Invert the cake onto a platter. Swirl the meringue decoratively over the top of the cake. Using a kitchen blowtorch, lightly brown the meringue, then serve.