Vollering grasps Tour de France Femmes lead with victory atop Tourmalet
Vollering, seventh overnight, pulled away in the final 6km of the 17km final climb in the Pyrenees to take the yellow jersey from teammate Lotte Kopecky (27).
The Dutch rider leads the overall standings by one minute and 50 seconds from Kasia Niewiadoma (28), who was second in the stage. Defending champion Annemiek van Vleuten (40) is third, but two minutes and 28 seconds back with only Sunday's 22.6km eighth-stage time trial to come.
Vollering started the short but brutal Pyrenean stage more than a minute behind race leader and Worx team-mate Kopecky and 12 seconds behind Dutch rider Van Vleuten.
The trio were part of an elite group that pulled clear on the first of two tough climbs, the Col d'Aspin. On the final foggy 17km final ascent of the Tourmalet, Niewiadoma attacked first.
With less than 6km to go, Vollering set off in pursuit, quickly passed the Pole and then surged away.
"I went full gas to the finish. I felt good," she said. "I kept on pushing."
She battled slowly across the finish line standing on her pedals, a shadow in the mist silhouetted by the headlights of a cortege of officials vehicles.
Niewiadoma finished second one minute and 58 seconds behind. Van Vleuten wobbled across the line at 2:34 in third place.
Vollering who had plopped on the tarmac panting, rose to her feet beaming to embrace team-mate Kopecky, who had finished sixth.
"It's amazing. You set dreams and goals," said Vollering. "I was nervous and the whole team was behind me and told me I could do it."
Vollering had dropped to seventh after she was hit with a 20-second penalty on Thursday for drafting behind the Worx team car that was deemed to be driving dangerously.
She had climbed a place before the start of Saturday's 90km mountain stage when Elisa Longo Borghini (31), who was fourth overall overnight, withdrew before the start.
The Italian veteran was suffering from a "skin infection on the upper left thigh", said her Lidl-Trek team and had to go to hospital on Friday at the end of stage six.
"The infection is now under control, but Elisa is still in a lot of pain."