Preheat the oven to 375 degrees F. Line 3 sheet pans with parchment paper.
In an electric mixer fitted with the paddle attachment, beat the butter, brown sugar, and granulated sugar on medium-high speed for 3 minutes, until light and fluffy. Scrape down the bowl with a rubber spatula. On low speed, add the vanilla, then the eggs, one at a time. Scrape down the bowl again.
Meanwhile, sift the flour, baking soda, and salt into a medium bowl. Mix in the oats. With the mixer on low, slowly add the flour mixture to the butter-sugar mixture. Don't overbeat it! With a rubber spatula, stir in the chocolate and cranberries until the dough is well mixed. With a 1 3/4-inch ice cream scoop (or two spoons), scoop round balls of dough onto the prepared sheet pans. Sprinkle lightly with fleur de sel. Bake for 10 to 12 minutes, until nicely browned. Serve warm or at room temperature.