Preheat oven to 375ºF (190ºC). Line the bottom of a 9 x 5-inch loaf pan with parchment paper. Grease and flour the insides.

In a medium-size bowl, whisk together the 1 3/4 cups (223g) flour, baking powder, baking soda and salt.

In a large bowl, cream the butter and brown sugar until light and fluffy. Beat in the egg, egg yolk and vanilla in 3 separate additions, making sure each one is fully incorporated before adding the next.

In a small bowl, whisk the milk and sour cream together.

Add the flour mixture to the batter in two additions, alternating with half of the milk mixture after each addition. Beat just until combined. Do not over mix.

Set aside a handful of chocolate chips for the top of the loaf. In a small bowl, toss the remaining chips with 1 teaspoon flour, making sure to coat them all, then fold them into the batter. This will help to prevent them from sinking. Transfer the batter to the prepared loaf pan. Top with the reserved chocolate chips.

Bake for 10 minutes. Turn the oven temperature down to 325ºF (165ºC) and continue baking until the loaf is golden brown and a toothpick inserted in center comes out clean, about 45-50 more minutes. Cool the loaf in pan for 10 minutes then turn the loaf out onto a cooling rack.