In a medium saucepan bring half-and-half to a boil; set aside and keep hot.
In a small mixer bowl beat egg yolks at high speed until thick and lemon-colored, about 2 minutes. At medium-high speed, gradually beat in sugar, cornstarch and flour until thick and smooth. On low speed beat in half-and-half. Return mixture to saucepan. Cook and stir over medium heat until thick and creamy, about 5 minutes. Remove from heat.
Stir in vanilla. Place waxed paper or plastic wrap directly on surface; refrigerate until chilled.
In a small saucepan over low heat melt chocolate and butter or margarine. Add milk; blend well. Remove from heat. Transfer to a small mixer bowl.
Beat in powdered sugar and vanilla until smooth. Add a little more milk if glaze becomes too thick to pour.
Spoon 2 to 3 tablespoons of filling in center of each crepe. Roll and place seam-side down on dessert plates. Drizzle about 1 1/2 tablespoons glaze over each. Serve immediately.