Preheat the oven to 325 degrees F. Grease a 9x5 inch loaf pan with butter, then sprinkle over a layer of sugar to coat and tap out the excess (you could also use butter and parchment paper to line the loaf pan).
In a medium bowl, whisk together the flour, baking powder, and salt, then set aside.
Place the granulated sugar and lemon zest in a large bowl, then use your hands or a spoon to rub them together until the sugar clumps and becomes fragrant, around 1 minute.
Add the softened butter to the bowl and, using a hand mixer or a stand mixer fitted with the paddle attachment, whip until light and fluffy, around 3 minutes.
Stream in the vegetable oil and whip for 1 minute more. Once combined, add in the eggs, one at a time, followed by the lemon extract and vanilla extract.
Add in around ⅓ of the dry ingredients to the creamed sugar mixture, mixing until just combined, followed by about ½ of the buttermilk. Continue alternating the dry and wet ingredients, ending with the remaining ⅓ of the flour and folding until just combined.
Using a silicone spatula, scrape the batter into the prepared loaf tin and smooth the top. Bake for 50 minutes to an hour, until a toothpick inserted in the middle of the cake comes out clean. If making the syrup, use a small toothpick or cake tester to prick 1 to 2 inch deep holes all over the surface of the cake once out of the oven.
Allow the cake to cool for 10 minutes before lifting out of the tin and cooling completely on a wire rack.
In the meantime, prepare the lemon syrup (optional). In a small saucepan, combine the lemon juice and sugar. Heat the mixture over medium-high heat and simmer until the sugar dissolves, around 3 minutes. Remove from the heat and allow to cool.
Once the loaf has cooled, brush it all over with the syrup (you don't have to use all of it).
To make the glaze, mix together the powdered sugar with around a tablespoon of lemon juice, stirring and adding more lemon juice as necessary until a runny consistency is reached. Spread the glaze over the top of the cake and allow to fully set before slicing and serving.