For custard: Scald half and half in heavy medium saucepan. Whisk yolks, sugar and flour in top of double boiler until smooth. Gradually whisk in hot half and half. Set over boiling water and stir until custard is very thick and mounds when dropped from spoon, about 6 minutes. Set top of double boiler over ice and chill custard, whisking occasionally. Mix in vanilla.
Combine whipping cream and espresso powder in large bowl and stir until powder dissolves. Beat to firm peaks. Add Scotch and beat until firm. Fold cream mixture into cold custard in 2 additions. (Can
be prepared 1 day ahead. Cover and refrigerate.)
For trifle: Place half of pound cake cubes in 3-quart trifle bowl or glass bowl. Sprinkle with 3 tablespoons Scotch and toss. Heat jam in heavy small saucepan until just pourable. Spoon half of jam over cake and spread. Top with half of custard. Top with 1/2 the raspberries, making sure some berries show at sides of bowl. Top with half of bananas. Place remaining pound cake cubes in another bowl. Sprinkle with 3 tablespoons Scotch and toss. Layer fruit over. Spoon remaining jam over and spread. Top with remaining custard, then with other halves of raspberries and bananas. Cover and refrigerate until set, at least 3 hours. (Can be prepared 1 day ahead).
Whip cream and sugar in large bowl to stiff peaks. Add 3 tablespoons Scotch and beat to firm peaks. Mound cream atop trifle. Garnish with fresh raspberries and chocolate.