1. Whisk dry ingredients: In a medium bowl, sift flour, cocoa powder, baking powder, salt, and espresso powder (if using). Stir in 3/4 cup chocolate chips. Set aside.

2. Beat wet base: In a large bowl, use a hand mixer on medium-high to beat eggs, egg yolk, granulated sugar, brown sugar, oil, and vanilla for 4-5 minutes until pale, thick, and ribbony. This incorporates air for chewiness.

3. Melt chocolate: In a small saucepan over low heat (or microwave in 20-second bursts), melt butter and remaining 1/4 cup chocolate chips, stirring until smooth. Let cool 2 minutes.

4. Combine wet mixtures: Slowly pour melted chocolate into egg mixture, mixing on low until just blended. Avoid deflating the batter.

5. Fold in dry: Gently fold dry ingredients into wet with a spatula until no streaks remain. Batter will be thick and glossy. Let rest 10 minutes for flavors to meld.

6. Scoop dough: Use a 1.5-tablespoon cookie scoop (or two spoons) to drop mounds 2 inches apart on sheets. Cookies spread, so space generously.

7. Bake: Place in middle oven rack. Bake 10-12 minutes until tops crackle and edges firm but centers stay soft. Rotate sheets halfway for even baking.

8. Finish fresh: Remove from oven. Immediately press 2-3 extra chocolate chips into each top and sprinkle sea salt. Cool on sheet 5 minutes, then transfer to rack.