Sydney Sweeney's all birthday-caked up for her sexy new lingerie drop ... turning up the heat and showing off her bangin' bod to plug her latest products.

The blonde bombshell shared a series of steamy sets as she fussed over baking herself a birthday cake in a new social media post.

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See for yourself ... she got a bit cheeky, dusting the flour off her hands and flaunting her assets in that lacy lingerie.

At one point, she went totally topless to show off those killer curves and amazing abs in tiny pink ruffled undies.

Sydney's a September birthday ... and with a new flip of the calendar only a few days away, she's getting on the promo train ... teasing a new collection dropping Sept. 1.

Alright, alright, Sydney. You have our attention!