Preheat oven to 350°F. Generously butter 13x9-inch baking dish.
PREPARE THE CAKE:
Beat ¾ cup sugar and egg yolks until light and fluffy, about 5 minutes. Fold in the milk, vanilla, flour and baking powder. In a separate bowl, beat the egg whites to soft peaks, adding the cream of tartar after 20 seconds. Gradually add the remaining ¼ cup sugar and continue beating until the whites are glossy and firm, but not dry. Gently fold the whites into the yolk mixture. Pour this batter into the buttered baking dish. Bake the cake until it feels firm and an inserted toothpick comes out clean, about 30 to 45 minutes. Let the cake cool completely in a baking dish. Pierce the cake all over with a fork, taking care to not tear it up.
PREPARE THE MILK SYRUP:
Combine all of the milk syrup ingredients in a mixing bowl. Whisk until well blended. Pour the syrup over the cake, spooning the overflow back on top, until it is all absorbed.
When ready to serve, dust the whole cake with cocoa powder. Cut a slice and plate it. Top with a dollop of whipped cream or a side of ice cream, and garnish with fruit.