Preheat oven to 375 degrees F (190 degrees C). Grease and flour 2 - 8 inch round cake pans and line bottoms with rounds of parchment paper. Sift together the cake flour, baking powder and salt; set aside.
In a large bowl, cream together 1/2 cup butter and 1 cup sugar until light and fluffy. Add the eggs one at a time, beating well with each addition, then stir in 1 teaspoon vanilla. Add the flour mixture alternately with 3/4 cup milk. Mix only enough to blend thoroughly; do not overmix.
Divide the batter between 2 - 8 inch pans. Bake in the preheated oven for 25 to 30 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.
To make the Pastry Cream Filling: In a small saucepan, heat 1 cup milk to the boiling point and remove from heat. In a heatproof mixing bowl, beat 3 egg yolks until smooth. Gradually add 1/2 cup sugar and continue beating until pale yellow. Beat in 1/4 cup flour. Pour the hot milk into the egg yolk mixture in steady stream, beating constantly. When all the milk has been added, place the bowl over a pan of boiling water so that the bowl is not touching the water, or pour the mixture into the top of a double boiler. Heat, stirring constantly, until thickened. Cook 2 minutes more, then remove from the heat. Stir in 1 tablespoon butter and 1 teaspoon vanilla. Let cool.
To make the Glaze: In the top of a double boiler, melt the chocolate with 2 tablespoons butter. When smooth, remove from the heat and beat in the confectioners sugar to make a thick paste. Add 1/2 teaspoon vanilla. Beat in a little of the hot water. If the glaze does not have a spreadable consistency, add more water 1 teaspoon at a time.
To assemble the cake, spread the cooled pastry cream over one of the cake layers. Place second cake layer over pastry cream and spread the chocolate glaze over the top using a metal spatula. Dust top with confectioners sugar. Refrigerate any leftover cake.