Preheat the oven to 350 degrees. Spray a loaf pan with non-stick baking spray (with the flour in it.) (You could alternatively line with parchment paper.)
In a medium mixing bowl, whisk the flour, cornstarch, baking powder, and salt together, then set aside.
In your mixer bowl, mix the sugar and lemon zest together for a minute. Add the butter and cream it with the lemon sugar mixture for 3-4 minutes.
Add your eggs and the extra yolk one at a time, beating after each addition.
Add in the canola oil, lemon juice and vanilla extract and mix until well combined.
Turn the mixer to low, add half of the flour, then the 1/2 cup of half and half, then the other half of the flour, mixing until just combined.
Remove the bowl from your mixer and gently stir, scraping the bottom to make sure everything is combined, then spread the batter in to the prepared loaf pan.
Bake the loaf for 45-50 minutes or until the top is golden brown and a toothpick comes out just about clean, (there might be a few moist crumbs.)
Remove the loaf from the oven, let it cool for 10-15 minutes, then loosen the loaf around the edges, remove the loaf from the pan and place it on a cooling rack until it is cool.