Preheat oven to 325º F.

Combine cookie crumbs, ¼ cup sugar, and butter in bowl; blend well. Press on bottom and 2-inch up sides of 9-inch springform pan. Set aside.

Combine 1 (8-ounce) package cream cheese and ¼ cup sugar; beat until fluffy. Add 1 egg and ¼ teaspoon vanilla extract; blend well. Stir in melted chocolate and ½ cup sour cream. Spoon over cookie crust.

Combine remaining (8-ounce) package cream cheese, brown sugar, and flour; beat until fluffy. Add 1 egg and ½ teaspoon vanilla extract; blend well. Stir in pecans. Spoon gently over chocolate layer.

Combine 5 ounces cream cheese and remaining ¼ cup sugar; beat until fluffy. Add remaining egg, and blend well. Stir in remaining 1 cup sour cream, and ½ teaspoon vanilla extract. Spoon gently over pecan mixture. Bake for 1 hour; turn off oven, and leave cheesecake in oven for 30 minutes. Partially open door of oven, and leave cheesecake in oven an additional 30 minutes. Let cool to room temperature on a wire rack. Chill at least 8 hours.

Chocolate Glaze : Combine chocolate and butter in top of double boiler; bring water to a boil. Reduce heat to low; cook, stirring occasionally, until chocolate melts. Remove from heat; add remaining ingredients, stirring until smooth. Spread warm glaze over cheesecake. Yield: 10 to 12 servings.