Advance Preparation: Crust can be prepared several hours in advance; it must chill for at least 30 minutes before it is filled. The filled pie must be refrigerated for at least 3 hours, or overnight, before serving.

Special Equipment: 9-inch pie plate, pastry brush, candy thermometer (optional)

1. Prepare the coffee base for the mousse: In a small saucepan, sprinkle the gelatin over 1/4 cup of the cold water, and set aside to soften about 3 minutes. Then place over low heat and stir until the gelatin is dissolved; do not boil. Remove the pan from the heat and whisk in the milk, 3 Tbsp of the sugar, the espresso of coffee powder, cocoa, cinnamon, and salt.

2. Return the pan to low heat and whisk for about 3 minutes, until the sugar is dissolved. Remove the pan from the heat and stir in the coffee liqueur and vanilla. Pour the mixture into a large heatproof bowl and set aside at room temperature.

3. Prepare the meringue: In a 1 1/2-quart saucepan, stir together the remaining 1/4 cup water, remaining 1/2 cup sugar, and the cream of tartar. Set over medium heat and cook, gently swirling the pan several times, until the sugar is dissolved. To prevent sugar crystallization, wash down the pan sides with a pastry brush dipped in cold water. If you have a candy thermometer, clip it to the pan. Increase the heat to medium high and boil without stirring until the thermometer reads 239 degrees to 242 degrees F, or until a drop of the syrup forms a soft ball when dropped in ice water.

4. While the syrup is cooking, begin to whip the egg whites in a medium bowl: Whip until medium peaks form.

5. When the syrup reaches the specified temperature, remove it from the heat, and gradually pour it over the whites while whipping them at medium-low speed. Pour the syrup in a steady stream between the sides of the bowl and the beaters (do not scrape in the hardened bits from the sides). Continue whipping until the whites feel cool and form stiff peaks, about 5 minutes. Set aside.

6. Prepare an ice water bath, with a tray or two of ice cubes in a large bowl, water, and a few sprinkles of salt. Set the bowl of coffee base in the ice water bath and stir until it chills and thickens to the consistency of raw egg whites. Don't let it set completely; if it chills too much and feels stiff, place it over a pan of hot water and stir or whisk briefly until smooth and creamy (like soft pudding).

7. Whisk about 1 cup of the cooled meringue into the coffee mixture to lighten it, then fold in the rest of the meringue.

8. In a clean medium bowl, using clean beaters, whip the cream until soft peaks form. Fold the whipped cream into the coffee-meringue mixture. Don't worry if a few streaks of white remain.

9. Turn the mousse into the chilled crust, and smooth the top. Refrigerate for at least 3 hours, or overnight. Just before serving, if desired, arrange a ring of chocolate-covered espresso beans around the rim of the pie.

(Continued in part 2)