Preheat the oven to 375?F. Grease a 9 x 13-inch glass baking dish with 2 teaspoons butter and set aside.
Combine the eggs and milk in a large bowl and beat with an electric mixer on low speed until frothy. Add 1 1/3 cups of the sugar and beat on high speed until the mixture is quite thick and pale yellow, 7 to 10 minutes.
Sift the flour, baking powder, and salt together into a medium bowl. Fold this mixture gently into the egg mixture. Gently stir in the melted butter and then transfer the batter to the prepared dish and bake in the center of the oven until risen and golden brown, about 30 minutes. Remove from the oven and let cool on a wire rack before proceeding.
Meanwhile, combine the strawberries, the remaining 2 cups sugar, Grand Marnier, and orange zest in a large bowl and toss to combine. Let stand at room temperature for 15 minutes, stirring occasionally, until the sugar is dissolved. Refrigerate, covered, until ready to assemble the dessert.
Combine the heavy cream with the confectioners' sugar in a large bowl and beat with an electric mixer or whisk until slightly thickened. Add the vanilla and continue to beat until the mixture nearly forms stiff peaks.
When ready to assemble the dessert, poke holes all over the cake with a cake tester or toothpick. Pour the strawberry mixture over the top of the cake, juices and all, spreading it evenly with a spatula and allowing the cake to absorb the juices. Top with the whipped cream and serve immediately, or refrigerate for up to an hour before serving.
Makes 12 to 16 servings