Prep: Preheat oven to 360°F. Line a 9x5 inch (OR 8x4 inch) loaf pan with baking parchment.
Cream ingredients: Place butter in a large mixing bowl and beat with a hand mixer using the beater attachments until creamy (you can also use a stand mixer with the paddle attachment). Add eggs and sugar and cream until light in color and fluffy. Add buttermilk, lemon zest, lemon juice and lemon extract and mix until combined (it's OK if it looks split and weird after adding buttermilk).
Add dry ingredients: Add flour, baking powder and salt to creamed ingredients. Mix on low with your mixer, until you have a smooth batter.
Bake: Pour batter into prepared pan. Bake for 45-55 minutes, or until a toothpick inserted comes out clean. Cool in the pan for 10 minutes before removing to a cooling rack to cool completely.
Glaze: Mix icing sugar and lemon juice until smooth and barely pourable (it's a thick glaze). Carefully spread on top of completely cooled cake.