Whipped cream is not getting thicken properly
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Is it chilled? Whipped cream whips up faster and more efficiently if everything is chilled. Have you added sugar to it already? Sweetened cream takes forever to whip.
A local baker told me that generally the problem is that most heavy cream/whipping cream is ultra-pasteurized and that makes it very difficult to whip properly. I do notice differences between brands so you may try switching.