Butter and flour the baking pan and line with a parchment paper sling to help lift the cake while cooling. If desired, Hold the parchment paper in place with metal binder clips.
Preheat oven to 325°F.
Cream butter and sugar. Cut the butter into large chunks and place in the bowl of a stand mixer fitted with a paddle attachment. Beat on medium speed to soften, about 2 minutes. Scrape down the sides of the bowl and add sugar. Beat the sugar and butter on medium-low speed until the sugar is fully combined with the butter. Increase speed to medium and continue creaming for 5-7 minutes, stopping to scrape down the bowl and the paddle 2-3 times. The butter and sugar will be fluffy and have a light texture.
Add eggs and vanilla. Add in the eggs ONE AT A TIME and beat for at least 60 seconds before adding the next egg. Finally, add vanilla paste. If the batter is looking curdled- no worries- this is normal.
Add flour and dry ingredients. Turn the stand mixture to low and add half the dry ingredients. Mix just until fully combined, then stop and scrape the bowl down. Use a silicone or rubber scraper to mix in any final bits of dry ingredients from the sides of the bowl or beater. Do not over mix! You will have a dry and dense cake.
Bake. Scrape the batter into the prepared loaf pan. Smooth with an offset spatula. Pro tip: Cut a stick of butter into a long, thin slice and place it down the center of the cake before baking. Bake on the middle rack in a 325°F oven for 65-75 minutes until a cake tester or bamboo skewer (do not test with a toothpick- it is too short) inserted in the center comes out nearly clean.
Cool. Set the cake pan on a wire rack to cool 15-20 minutes, then use the parchment sling to lift the cake out of the pan to finish cooling. Let cool completely before adding icing.