Preheat the oven to 375°F. Line several large 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. (Alternatively, a hand-held mixer can be used)

Meanwhile, sift the flour, baking soda, and salt into a medium bowl. With the mixer on low, slowly add the flour mixture to the butter-sugar mixture. Be cautious not to overbeat it.

Add the oats and with a rubber spatula or wooden spoon, stir well to fully incorporate. Then add the chocolate chunks along with the raisins. Continue stirring until the dough is well mixed.

With a 1½-tablespoon ice cream scoop (or two spoons), scoop round balls of dough onto the prepared sheet pans. Sprinkle lightly with flaky sea salt. Bake for 10 to 12 minutes, until nicely browned. Serve warm or at room temperature.

Baked cookies can be stored in airtight container, then reheated for 5 minutes at 350°F.