Recipe(tried): Classic Boston Creme Pie - Help! What am I doing wrong?

YIKES! HELP! BAKING PROS: What am I doing wrong? I made this recipe -- a classic Boston Creme Pie by Chef Jamie Roraback of the Connecticut Culinary Institute -- but the cake part fell just after I took it out of the oven. It was brick hard. It also had "tunnels" in it. I sifted the flour several times, just like it said. Also, when it came to making the custard filling -- it didn't seem sweet enough. OR silky enough. I think I could/should have used a flat, sauce-making whisk instead of a long thin one. But it still wasn't very silky. Did I cook it too fast, or what? Would you mind giving me some advice? It's my boyfriend's favorite cake, and I want to do it right. Here's the recipe:

Classic Boston Creme Pie
By Chef Jamie Roraback
Makes an 8 Inch Pie

CAKE:
3 eggs, carefully separated so no yolks get into the whites
1/3 cup granulated sugar
1/8 tsp. cream of tartar, or substitute white vinegar or lemon juice
1 tsp. pure vanilla extract
1/2 cup cake flour, measure before sifting, sift twice before adding
2 tbsp. melted butter
CREAM FILLING:
3 eggs
1/2 cup granulated Sugar
1/4 cup cake flour
2 cups milk
1 tbsp. butter
1 tbsp. pure vanilla extract
CHOCOLATE GLAZE:
1 cup heavy cream
8 oz. bitter or semi-sweet chocolate, chopped
TO ASSEMBLE:
1/2 cup almonds, toasted and ground in food processor until fine
1/2 cup white chocolate, melted for decoration

Preheat oven to 375 degrees. Butter and flour one 8 inch round cake pan. For added non-stick protection, place a circle of parchment paper on the bottom of the cake pan.

To make the cake, place egg yolks in a mixing bowl with half of the sugar, place over a pot of simmering water and whisk until warmed and sugar is dissolved, do not cook eggs. Combine the egg whites with the remaining sugar and cream of tartar, place over a pot of simmering water and whisk until warmed and sugar is dissolved, do not cook egg whites. Using an electric mixer with a whisk, whip the yolks until thicker, lightened and the color becomes a very pale yellow, about 3 minutes. Whip the whites (make sure no egg yolks get into the mixture) until medium stiff peaks. In a larger bowl, combine the whipped yolk and white mixtures with the vanilla extract, stirring gently just until combined. Add the sifted cake flour, fold in just until combined, then stir in the melted butter. Pour into the cake pan, tap down to level, place on a cookie sheet and bake in the oven for about 25 minutes until a toothpick comes out clean and the cake springs back when lightly touched. Let cool on a wire rack for 10 minutes, invert to unmold and let cool completely.

To make the cream filling, place the eggs in a mixing bowl. Sift the sugar and cake flour into the eggs. Whisk until totally smooth. Gradually whisk in the milk until smooth. Place in a heavy bottomed, stainless steel pot and cook over medium heat while whisking constantly. When the mixture is at a near boil, whisk even faster to make smooth. Let the mixture come to a bubble, remove from heat and stir in the butter and vanilla. Pour the mixture into a shallow dish, cover with plastic wrap and refrigerate until cool.

To make chocolate glaze, bring the cream to a boil and whisk in the chopped chocolate until smooth. Reserve warm.

To assemble, trim the top of the cake off until level. Slice the cake in half horizontally. Place the bottom half with the browned side up on a wire rack with a cookie sheet underneath. Pour over the chocolate glaze, evenly coating the top and the side. Allow to cool until slightly set, then drizzle on the melted chocolate in any decorative pattern if desired. Place the remaining cake layer on a serving plate and spread with the cream filling. Lightly ice the side of the cake layer with some of the cream filling and adhere on the toasted almonds. Place the chocolate coated cake evenly on top of the cream topped cake. Cake can be sliced and served, or refrigerated and served later.