。
She whipped the cream for dessert.
Literal
She [topic-は] dessert [for-用に] cream [object-を] [whipped-up-泡立てた].
デザート用 uses the productive suffix ~用 ('for use as / designated for'), attached to a noun to form 'X-purpose, for-X.' Other examples: 子供用 ('for children'), 業務用 ('commercial use'), 観光用 ('for tourists'). The に turns the resulting noun into an adverbial purpose phrase. 泡立てる ('whip, beat into foam') is a delightfully literal Japanese verb — 泡 ('foam') + 立てる ('make stand up') = 'make foam rise up.' Uses include whipping cream, beating egg whites into meringue, and creating soap suds.