Preheat oven to 350F (regular bake setting/non convection).
Line an 8x8-inch baking pan with parchment paper for easy removal (or greased well). Set aside.
In a large bowl with an electric mixer or in the bowl of a stand mixer fitted with the paddle attachment, cream together the room temperature butter and white sugar on medium speed until lightened in texture and colour, about 2 minutes. Beat in the eggs, one at a time, mixing well between additions and scraping down the bowl a couple of times, as needed. Mix in the lemon zest, lemon juice and vanilla.
Mix in the flour, together with the salt, mixing just until combined and smooth. Pour batter into prepared pan and smooth the top.
Bake 23-25 minutes, or until a tester comes out clean. Remove from oven and allow to cool completely in the pan before glazing.
To glaze, combine the icing sugar and lemon juice. Stir well until perfectly smooth. The glaze should run off a spoon easily. *You may need to slightly adjust with more lemon juice, if too thick or a touch more icing sugar if too thin. Pour over the cooled blondies and use a spatula to spread it over the top completely. *Tip! Gently jiggle the pan back and forth after spreading, to smooth and even out the glaze. Allow the glaze to set at room temperature, about 30 minutes. Once the glaze is set, remove from pan and cut into squares. (I like to cut into 16 squares).
Store in an airtight container at room temperature for several days. These should also freeze, though the glaze may become moist after freezing and thawing. For best results, glaze after freezing and before serving.