Preheat oven to 325ºF. Generously grease a 9×5 loaf pan and line with a sheet of parchment paper fitted to the length of the pan. Leave a small overhang of parchment on both sides to help lift cake out of the pan later. Set aside until needed.

Combine milk and vinegar/lemon juice, and set aside to sour.

In a medium bowl, whisk together flour, cornstarch, baking powder, and salt. Set aside.

In a separate large mixing bowl beat butter until creamy. Beat in oil and yogurt, then the sugar, mixing until creamy, scraping down the sides as necessary. Mix in vanilla.

Begin to add flour, a cup at a time, alternating with sour milk. Scrape down sides of the bowl and mix just until batter is smooth.

Pour batter into prepared pan and smooth the top. Bake on the middle rack for 60–70 minutes, or until the center is set and a toothpick inserted comes out clean. Bake time will vary depending on your oven and the pan you use, so begin checking on it at around 55 minutes.

This cake is delicate right after baking. Let cake cool for 15–25 minutes in the pan, then run a knife along the edges to release the cake from the pan. Use the excess parchment paper as handles to gently lift the cake out of the pan.

Place cake on a wire rack to cool completely.

Cake is more crumbly when it is warm, but firms up as it cools. Make it the night before serving for best results. This cake is delicious served with fruit and whipped cream! Serves 8–10.