Preheat oven to 350°F (175°C). Grease and line loaf pan.
Make streusel by mixing flour, brown sugar, cinnamon, and butter until crumbly.
Whisk flour, baking powder, baking soda, and salt together.
Beat butter and sugar until light and fluffy.
Add eggs one at a time.
Mix in half the dry ingredients.
Add sour cream, oil, and vanilla.
Add remaining dry ingredients and mix until combined.
Divide batter in half and mix cinnamon into one portion.
Alternate batters in loaf pan and swirl gently.
Top with streusel.
Bake 60–65 minutes or until toothpick comes out clean.
Cool completely.
Mix glaze ingredients until smooth and drizzle over loaf.