FOR THE PASTRY CREAM: In medium saucepan over medium heat, heat half-and-half until just simmering. In medium bowl whisk yolks, sugar, and salt until smooth. Add flour to yolk mixture and whisk until incorporated. Remove half-and-half from heat, and whisking constantly, slowly add ½ cup half-and-half to yolk mixture to temper. Whisking constantly, pour tempered yolk mixture into half-and-half in saucepan. Return saucepan to medium heat and cook, whisking constantly, until slightly thickened, about 1 minute. Reduce heat to medium-low and continue to simmer, whisking constantly, for 8 minutes. Increase heat to medium and cooking, whisking vigorously, until bubbles burst on surface, 1-2 minutes. Take saucepan from heat; whisk in butter and vanilla until butter is completely melted. Strain pastry cream through fine-mesh strainer set over medium bowl. Lightly grease parchment or plastic wrap with nonstick cooking spray and press it directly on surface of pastry cream. Refrigerate until set, at least 2 hours and up to 24 hours.
FOR THE CREPES: In large bowl sift together flour and salt. In small bowl whisk together milk, eggs, water, and melted butter. Whisk egg mixture gradually into flour. Place large, fine strainer over medium bowl and pass batter through strainer. Cover bowl with plastic wrap and chill at least 2 hours, or up to 2 days.
Gently whisk batter. Heat 6-7-inch crepe pan or heavy skillet over medium-high heat. Brush bottom of pan and side very lightly with butter (butt should sizzle when it hits the pan). When butter stops sizzling, pour 2 ½ tablespoons (use ¼-cup measure just over half full) batter into pan. Do this by tilting heated pan just slightly to the left and begin pouring the batter. Continue to pour batter in a steady stream as you twirl the pan slowly counterclockwise until the crepe is formed. Cook until crepe is nicely browned on bottom, 30 seconds-1minute. Loosen crepe from pan with table knife or metal icing spatula and flip. Cook until nicely browned on other side, about 30 seconds longer.
Move cooked crepe to a large plate and repeat cooking process with remaining batter, brushing pan as needed, every 2-3 crepes or so.
TO ASSEMBLE: Place 1 crepe on cake plate. Spread 2 tablespoons of pastry cream into a thin layer over crepe. Cover with another crepe and repeat to make a stack of about 18 crepes. Place crepe cake in refrigerator while you make the chocolate glaze.
FOR THE CHOCOLATE GLAZE: In small saucepan over medium heat bring cream and corn syrup to a simmer. Remove from heat and add chocolate. Whisk gently until smooth, 30 seconds. Let stand, whisking occasionally, until slightly thickened, about 5 minutes.
TO FINISH CREPE CAKE: Pour glaze onto center of cake. Use an offset icing spatula to spread glaze to edge of cake, letting excess drip decoratively down sides. Place crepe cake in refrigerator for at least 3 hours or up to 24 hours before slicing and serving.