For pastry cream: Combine cream and milk in medium saucepan; bring to simmer. Remove from heat. Whisk sugar, egg yolks, flour, amaretto, vanilla, and salt in large bowl until smooth (mixture will be thick and pasty). Gradually whisk hot cream mixture into yolk mixture. Return mixture to saucepan. Whisk over medium heat until pastry cream boils, thickens and is smooth, about 6 minutes. Transfer pastry cream to bowl. Press plastic wrap directly onto surface of pastry cream; refrigerate overnight.
For pears: Position rack in center of oven and preheat to 400°F. Toss pear halves, 1/3 cup sugar, and lemon juice in large bowl. Place pears, cut side down, on heavy large rimmed baking sheet; pour sugar mixture from bowl over pears. Roast pears until tender and golden brown in spots, turning occasionally, about 40 minutes. Cool. Cut pears into 1/2-inch pieces; place in bowl along with any juices from baking sheet. (Pears can be made 1 day ahead. Cover and chill.)
Arrange 13 to 14 ladyfingers in bottom of 8-inch-diameter, 3-quart trifle bowl, trimming to fit tightly. Sprinkle 1/2 cup crushed amaretti cookies over. Dot with 1/4 cup fruit spread. Top with 1 cup roasted pears. Drizzle 1 tablespoon brandy and 1 tablespoon amaretto over. Spread 1 cup pastry cream over. Repeat layering 2 more times with ladyfingers, amaretti cookies, fruit spread, pears, brandy, amaretto, and pastry cream. Top with 13 to 14 ladyfingers; sprinkle with remaining brandy and amaretto. Spread remaining pastry cream over top. Cover and refrigerate until cold, about 4 hours.
Beat cream, powdered sugar, and vanilla in large bowl until peaks form. Spread 1 1/2 cups whipped cream over top of trifle. Spoon remaining whipped cream into pastry bag fitted with medium star tip. Pipe whipped-cream rosettes around top of trifle. Garnish with sliced almonds and mint sprigs, if desired. Refrigerate up to 6 hours.
* Amaretti cookies are available at Italian markets and some supermarkets.