Rub the lemon zest with the sugar using the back of a spoon or your hands. This will help coat the sugar with the essential oils in the lemon zest, giving it an extra lemony flavor.
Replicate a double boiler by adding about ½ inch of water to a small pot and bringing it to a simmer. Combine all the lemon curd ingredients in a heat-proof medium and set it over the pot with simmering water.
Whisk for 5-7 minutes until it thickens.
Set aside and let it cool
For the loaf
Preheat the oven to 350 °F.
Rub the lemon zest with the sugar using the back of a spoon or your hands.
Whisk the melted butter, oil, and sugar. Add eggs and vanilla and combine. Add the buttermilk and combine.
In a separate bowl, mix the dry ingredients. Then add them to the wet ingredients and fold until combined.
Grease a 9x5 loaf tin and add 1/3 of the batter. Then add half of the lemon curd and top it with another third of the batter. Add the remaining lemon curd and top it off with the remaining batter.
Bake for 40 minutes and cover the loaf with aluminum foil. Bake for an additional 15-20 minutes or until top springs back when touched.
For the glaze
Mix both ingredients once you are ready to pour the glaze over the loaf.