Preheat the oven to 325°F (160°C), then grease an 8x8' pan with butter and dust it with cocoa powder (or flour) [a 9x9' pan would also work, but your cake will be shorter and flat].
In a small bowl, whisk together the flour, cocoa powder, salt, and baking soda until well-combined, and set aside. In a large bowl, cream your room temperature butter with the sugar until fluffy, scraping down the sides of the bowl as needed.
Then add the vanilla extract and eggs one at a time, incorporating each one well before adding the other.
Add in the sour cream until just combined.
Slowly pour in the dry ingredients, scraping down the bowl several times & pausing if needed, until the dry ingredients are just combined— the batter will be very thick, but if you overbeat it, the cake may lose some of its moistness, especially if you're making a gluten free chocolate pound cake.
Once the dry ingredients are incorporated, pour in the milk and mix until incorporated, then lightly blend or fold in the chocolate chips (if using).
Scrape the batter into your pre-floured pan and tap it or shake it to get the batter to settle evenly; you can also use your spatula to lightly push it around the pan, and then put it in your preheated oven for 50 to 60 minutes. Don't open the oven to start checking it until at least 45 minutes into baking, and remove it from the oven once a knife or toothpick comes out clean. If you're going to make a chocolate glaze, while the cake is baking is a good time to make it; alternately, you can dust your gluten-free sour cream chocolate pound cake with either cocoa powder or confectioner's sugar.