In a large mixing bowl, cream together the butter and granulated white sugar with an electric hand mixer on high speed until fluffy, about 3 minutes. (If you want to use a stand mixer, use the paddle attachment.)
1 1/4 cups (250 g) granulated white sugar, 1/2 cup (112 g) unsalted butter, softened
Add in the eggs and vanilla and mix on medium-high speed until pale in color and fluffy, 1-2 minutes.
3 eggs at room temperature, 2 tsp vanilla extract or bean paste
Add in the milk and sour cream and mix on medium-low speed just until combined. (The mixture will look a little curdled at this point, but don't worry.)
1/2 cup (120 ml) whole milk, at room temperature, 1/2 cup (122 g) sour cream, at room temperature
Add the dry ingredients to the wet ingredients a little bit at a time, mixing on low then medium-low speed just until combined.
Add in the chocolate chips and fold them into the batter with a rubber spatula.
1 cup (190 g) mini chocolate chips
Pour thecakebatter into the prepared loaf pan and bake it for 64-67 minutes, or until a toothpick comes out with just a few moist crumbs from the center.
Let the loaf cake cool in the pan for 30 minutes. Carefully pull up on the parchment paper to remove it from the pan. Transfer the loaf to a wire rack to completely cool.
For the Chocolate Ganache
While the loaf cake is finishing cooling, make the ganache. Add the chocolate chips to a medium sized, heat-safe bowl. Add the heavy cream to a small sauce pan and heat it just until boiling. Pour the cream over the chocolate and let it stand for 1 minute. Then stir to combine the chocolate and cream together.
1/2 cup (95 g) semi-sweet chocolate chips, 1/2 cup (120 ml) heavy cream
Once the loaf is completely cooled, pour the ganache on top of the loaf. Spread it evenly with a small off set spatula. Sprinkle with chocolate chips if using.You can wait until the ganache is set, or serve the cake right away!