Preheat the oven to 350°F and spray a 9x5-inch loaf pan with non-stick cooking spray; set aside.
In a large bowl with a hand mixer, cream together the butter and sugar until light and fluffy.
Add in the eggs and vanilla and mix just until combined then mix in the sour cream and milk until incorporated; set aside.
In a separate large bowl whisk together the flour, baking powder, baking soda, salt, and cinnamon.
Add the dry ingredients into the wet ingredients and stir in until just combined and no flour streaks remain.
Lastly, fold in the sprinkles but do not overmix them or they could bleed into the batter.
Spread into the prepared loaf pan and bake for about 60 to 70 minutes or until a toothpick comes clean from the center and the top is just golden. Remove from the oven and cool in the pan for 5 minutes then transfer to a wire rack to cool completely.
Meanwhile, make the glaze by whisking together the powdered sugar, heavy cream, and vanilla. Spread the icing over the cooled bread and smooth out with a rubber spatula.
Sprinkle with extra sprinkles if desired then let set then slice and serve.