These Chocolate Truffle Cookies are deeply chocolatey with cocoa and sea salt, without being cloyingly rich. A puddle of chocolate on top guilds the lily.
Add butter and sugar to bowl of standing mixer. Beat on medium-high speed until very light and fluffy, about 3 minutes. Scrape down sides of bowl then beat in eggs, one at a time, then vanilla. With mixer speed on low, slowly add the flour mixture, and beat until combined. Stir in the chocolate chunks, reserving a handful for topping cookies.
Preheat oven to 350ºF. Roll dough into 1" balls and transfer to parchment-lined baking sheets, leaving 2" space between cookies. Press a chunk of chocolate into the top of each. Bake 6-8 minutes, until slightly puffed and starting to crackle at edges. Cookies should still be soft and slightly underbaked. Sprinkle hot cookies with flaky salt then let cool 5 minutes on baking sheets then transfer to wire racks to cool completely.