What drink to pair with afternoon plum pie?

Prosecco + slivovitz garnished with mint . . . . . ;o)

Limoncello, straight or top it with a little setlzer or prosecco and a spring of basil or thyme. If you don't want alcohol, how about iced espresso with a scoop of Vanilla ice cream and a drizzle of caramel (see photo)

I'd offer both - coffee or tea, hot or iced (maybe with option of spiking it) and Champagne or Prosecco.

I prefer Prosecco - I find Champagne a bit heavy in warm weather - but a Kir Royale, using the standard Cassis or even a plum syrup/liqueur, would be nice with the fruit pie.

If it's me you're serving, that would be coffee (or tea), but I realize you probably mean alcohol-based :)

Prosecco is good but maybe try this for something a bit stronger https://food52.com/recipes/13206-voila-l-ete-the-french-75 I don't drink these anymore myself but it's one of my most saved contributions.

Champagne