4 Tbsp butter
1 cup sugar
2 tsp baking powder
1 tsp baking soda
2 tsp cinnamon
1 tsp salt
1 1/2 tsp vanilla
2 eggs
1 cup buttermilk (or 1 cup vinegar+milk substitution)
2 cups flour
2 Tbsp butter
1 tsp cinnamon
2 Tbsp brown sugar
Heat oven to 350. Spray a 9×5 loaf pan with nonstick cooking spray. (Optional: put some extra sugar and cinnamon in the bottom and up the sides of the loaf pan.)
Cream butter and sugar together in a stand mixer. Add baking powder, baking soda, cinnamon, and salt and mix together. Add vanilla and eggs and mix. Pour the buttermilk in slowly while mixer is running. Add flour 1 cup at a time and mix until you have a smooth batter. Pour into loaf pan.
In empty mixer, combine butter, sugar, and cinnamon into a paste. Dot the loaf with bits of the paste and push them down into the pan.
Bake on a sheet pan (just in case there’s any overflow) in the middle of the oven. Start checking on it after 45 minutes, but it will probably take closer to an hour.