Preheat the oven to 180ºC (350ºC). Line a 9-inch x 5-inch (23cm x 13cm) rectangle loaf baking pan with parchment paper. Set aside. NOTE: Alternatively, if you have a quality non-stick pan, liberally grease it with melted butter and dust it with a light layer of flour. This will leave your finished loaf with smooth edges.
In a medium size mixing bowl, add flour, baking powder, baking soda, salt, poppy seeds, and lemon zest. Whisk until well combined. Set aside.
In a large mixing bowl, using either electric hand beaters or a stand mixer with the paddle attached, add softened butter to the bowl.
Beat butter for a few seconds until creamy and broken up (this makes it easier when the sugar is added so it won't fly out of your bowl with the beater running).
Add sugar and beat on medium-high speed for 2 minutes, scraping down the sides as needed.
Add eggs one at a time, beating after each addition for 15 seconds. Scraping down the sides as needed.
Pour in milk, yogurt, lemon juice, and vanilla. Beat for 20 seconds until well combined. Scrape down the sides again.
Add half of the dry flour mixture and beat for a few seconds until just combined. Scrape down the sides.
Add the remaining flour and beat until just incorporated, ensuring not to over-beat, just until the pockets and streaks of flour have mixed through. TIP: If some excess flour is still visible around the sides of the bowl, gently fold it in with a spatula. If you over-mix, the loaf can turn tough and dense.
Pour into the lined pan and smooth out the top with a spatula.
Bake for 40-43 minutes, or until a skewer inserted into the middle comes out clean and the top is set and no longer wobbly.
Remove from the oven and allow to cool in pan for 10 minutes.
Carefully remove from the pan and transfer to a wire rack to cool completely.