For ice cream: Line 9-cup charlotte mold or 9-inch-diameter soufflé dish with double-thick layers of plastic wrap, extending over sides; place mold in freezer.
Mix half and half and cream in large saucepan; scrape in seeds from vanilla beans; add beans; bring to simmer; whisk yolks and sugar in large bowl to blend; gradually whisk in hot half and half mixture; return mixture to same saucepan and stir over medium-low heat until custard thickens and leaves path on back of spoon when finger is drawn across, about 8 minutes (do not boil); strain into large bowl; dvide custard equally between 2 medium bowls; add espresso powder and spices to custard in 1 bowl, stirring until espresso powder dissolves; cover and chill both custards until cold.
Process coffee-spice custard in ice cream maker according to manufacturers instructions; spoon ice cream into mold; using back of spoon and working quickly, spread ice cream over bottom and up sides of mold, leaving center hollow (you may need to freeze ice cream for a while if it becomes too soft and starts to melt down the sides before molding); feeze until firm, about 1 hour; using back of spoon, respread ice cream up sides of mold and even with top rim; place mold in freezer.
Process plain custard in ice cream maker according to manufacturers instructions; add cookie crumbs during last 1 minute of processing; spoon ice cream into center of mold, filling completely (reserve any remaining ice cream for another use); cover bombe; freeze overnight (can be made up to 1 week ahead; keep frozen).
For syrup: Stir sugar and ¼ cup water in medium saucepan over low heat until sugar dissolves; increase heat and boil without stirring until syrup turns deep amber, occasionally swirling pan; add brandy and remaining 3 tblsps water (stand back!); stir over low heat until caramel syrup is smooth; cool (can be prepared 1 day ahead; cover tightly and let stand at room temperature).
Whip cream in medium bowl to stiff peaks; spoon whipped cream into pastry bag fitted with medium star tip; unmold bombe onto serving plate; peel off plastic; pipe columns of cream up sides of bombe; pipe more cream on top of bombe; serve with syrup.