I had thought of Corsican mint (Mentha requienii); I use to grow it as an annual here in zone 4, as the seed seemed to jump around in my pots. But it was really tiny; leaves were only 2mm (1/16th inch), flowers even smaller. Now on the web I see it can grow much larger, but I still have strong reservations. The flower, in all its parts are unmistakeably veronica, in my opinion. See how the stamens and sepals are completely different in Mentha requienii? Corsican mint has a very strong smell, like creme de menthe liqueur. If it really has a unmistakeable mint smell, that must be what it is, bu I am very surprised. Mine did look "white" until I look very very close. If it is a mint, than
each flower must come directly from the main stem. If it is a veronica, each flower can come directly from the leaf stem too, or flowers can be connected to each other before connecting to the main stem.
Veronica gentianoides for comparison, but not your plant: