Preheat the oven to 350 ℉ (177 ℃) and grease and line a 1 pound baking pan with parchment paper.
In a medium sized bowl, rub the sugar with the lemon zest between your fingers until fragrant.
Beat the butter with the sugar on medium speed until creamy and fluffy.
Add the vanilla and the eggs, one at the time. Mix well inbetween.
Scrape down the sides of the bowl and add the sour cream, oil, milk, and lemon juice. Beat on low speed until incorporated.
Sift the flour, baking powder and salt. Gently fold or mix on low speed until just combined. Do not overmix.
In a small bowl, coat the raspberries with the cornstarch and toss.
Either fold in the raspberries to the batter, or layer the batter in the baking pan with the raspberries. The latter method will result in less "bleeding" from the raspberries.
Bake for 45 minutes to 1 hour in the oven or until a wooden skewer comes out clean (some crumbs are ok).
Once the raspberry loaf cake is finished baking, take it out, cover with a clean kitchen towel and allow to cool.