Melt the butter and 3/4 cup of chips in the saucepan over low heat for 3 to 4 minutes, stirring constantly, until smooth and glossy with no chip pieces left.

Whisk in both sugars for 1 minute, until thick and shiny (it will feel slightly gritty).

Cool the pan for 5 minutes, until the side feels warm but not hot and steam stops.

Whisk in the eggs, yolk, and vanilla for 1 full minute, until the batter is thick and falls from the whisk in ribbons.

Sift the cocoa, flour, baking powder, salt, and espresso powder over the batter. Fold for about 30 seconds, stopping when the last flour streak disappears. The batter looks like soft, thick frosting.

Fold in the remaining 1/2 cup of chips. Scrape the batter into the pan and smooth the top, so the pan is about half full.

Bake on the center rack for 38 to 44 minutes, until the edges pull from the pan, the top looks shiny and cracked, and a toothpick shows moist crumbs with no wet batter.

Cool in the pan on the rack for 20 minutes. Run a knife around the edge, lift the cake out, peel off the parchment, and cool 40 more minutes, until fully room temperature.

Microwave the cream in a glass measuring cup for 45 to 60 seconds, until small bubbles form at the edge and steam rises.

Pour the hot cream over 1 cup of chips in a bowl. Wait 3 minutes, stir slowly for 1 minute, then rest 10 minutes, until it thickens to warm pudding texture.

Pour the ganache onto the center of the cake and spread it toward the edges. Set 15 minutes, until glossy and a finger leaves no mark. Add flaky salt if using.