2 1/4cupsall purpose flour, measured with the spoon and level method
1/4teaspoonsalt, *reduce to a pinch if using salted butter
2-3Tablespoonslemon juice, or as needed to thin
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Remove the butter, egg and milk from the fridge and allow to come to room temperature before starting the prepare the batter. Be sure the butter is just at room temperature (which is about 68F). Do not melt the butter or try to soften in a microwave.
Preheat oven to 375F (regular bake/not fan assisted) with rack in the centre of the oven.
Grease a 9x5 or 4x11 loaf pan with cooking spray or baking spray and line the bottom and long sides with a sheet of parchment paper, allowing the long side of the parchment to overhang the edges by about 1-inch (to use as handles to lift the baked loaf out of the pan.) I haven't tested this loaf in an 8x4 loaf pan. It will work, though I'm not sure if all the batter will fit. If that's your only option, be sure to fill the pan only about 2/3 full, which may not be all the batter.
In a medium bowl, whisk together the flour, baking soda, baking powder, salt and poppy seeds. Set aside.
In a large bowl with an electric mixer or the bowl of a stand mixer fitted with the paddle attachment, cream together the room temperature butter with the white sugar at medium speed, until light and fluffy, about 2 -3 minutes. Scrape down the bowl with a rubber spatula. Add the egg and beat in well. Add the milk, vanilla lemon zest and lemon juice and mix in. Finally, add the Greek yogurt and mix in.
Add the flour mixture to the bowl, mixing at low speed until combined well. Add the poppy seeds, then give it a brief mixing at medium speed (5-10 seconds is all it needs).
Spoon the batter into the prepared pan and level the batter. You can mound the batter slightly by running a spatula around the outside edges, so that the centre is a little higher (refer to Step-by-Step photos to see this).
Baked in preheated oven for 40-50 minutes, or until golden and a tester inserted in the middle of the loaf comes out clean.
Remove from oven and let cool in pan 10 minutes, then remove the loaf from the pan by pulling up from the parchment paper. Place on a cooling rack. Fold down the sides of the parchment and allow to cool a bit further before removing and discarding the parchment. Cool completely on wire rack before glazing.
For the glaze, add the icing/confectioners' sugar to a small bowl. Add lemon juice to the icing sugar, 1 Tablespoon at a time, stirring well after each addition, until you have a thin glaze. Drizzle glaze over cooled loaf.
Be sure to read the Ingredient Notes above for substitution suggestions. You'll also find Step-by-Step photos there, as well as a few Baker's Tips.