Preheat oven to 350°F. Grease bottom and sides of an 8x4" loaf pan and line the bottom with a rectangle of parchment paper. Sift flour, baking powder, baking soda, and salt together in a bowl and set aside. Bring 2 inches of water to a boil in a small pot. Fill a separate small bowl with ice water.Blanch and shock rosemary sprig in boiling water for 45 seconds, then remove it to the ice bath for 15 seconds. Repeat one or two more times until rosemary leaves are flexible and slightly less firm but still green.Remove rosemary from the final dip in the ice bath and place it on a paper towel to dry. Set aside.
Cream butter and sugar together in the bowl of a stand mixer until light, pale, and fluffy. Scrape down the sides of the bowl a few times throughout this process. It may take a few minutes, don't rush it!
Add eggs one at a time, beating well and scraping down the sides of the bowl after each one to ensure they're fully incorporated. When all three eggs have been added, beat for an additional minute to emulsify until smooth and pale.Even done correctly, the mixture might look slightly curdled, but that's okay. Add about a third of the flour mixture to the mixer and beat on low speed to incorporate. Scrape down the sides of the bowl. Slowly drizzle in half the buttermilk with the mixer running. Then add another third of the flour mixture, followed by the rest of the buttermilk, and the rest of the flour mixture, always scraping down the sides and bottom of the bowl between additions.Once everything has been added, beat on medium speed for 1 minute.
Mince rosemary and toss mini chocolate chips with 1-2 tablespoon of flour, then stir both into the batter just until evenly distributed.
Pour batter into prepared pan. Bake immediately, approximately 50-60 minutes, rotating after about 40 minutes for even browning.When a knife inserted in the center comes out clean, it's done.
Remove from the oven. Run a knife around the edges, then let cool in the pan for 5-10 minutes before turning it out onto a cooling rack. Cool completely before slicing.