It would be essentially the same thing as a grid black start, except that the first breaker to close has the European grid on its primary side, instead of a freshly started generator under your control.
The complex process of configuring the transmission network to bring grid power to each power plant in succession is the same.
The continental part of the EU runs on one synchronized grid. The Nordics (except half of Denmark and, uh, Iceland, Greenland etc) runs on a separate synchronized grid.
https://en.wikipedia.org/wiki/Continental_Europe_Synchronous...
The entire EU runs on one synchronised grid so from that perspective a single 'province' went offline, not the grid.