Preheat oven to 325°F (163°C). Grease and flour two 8 x 4-inch loaf pans.

In a large bowl, beat the room-temperature butter and sugar together until light and fluffy (about 3–5 minutes with a stand mixer or a little longer by hand).

Add eggs one at a time, mixing until each is incorporated, then stir in the vanilla until smooth.

In another bowl, whisk the flour and baking soda until evenly combined.

With mixer on low, add about one-third of the dry mixture to the butter mixture. Mix briefly, then pour in about half the buttermilk. Continue alternating—dry, wet, dry—ending with the dry ingredients. Mix only until just combined; don’t overwork the batter.

Divide the batter evenly between the two prepared loaf pans and smooth the tops with a spatula.

Bake at 325°F for 60–70 minutes. Rotate the pans halfway through baking to ensure even browning. A toothpick inserted in the center should come out clean or with a few moist crumbs.

Let loaves cool in their pans for 10 minutes, then turn them out onto a cooling rack to cool completely.

Wrap tightly in plastic wrap and chill in the refrigerator overnight for the cleanest slices.