Preheat the oven to 180C/350F.
In a separate bowl, stir together flour, baking powder and salt, set aside.
Next, beat softened butter, lemon zest and sugar together with a standing or hand mixer. Add eggs and mix to combine.
Add lemon juice and mix to combine. The mixture will start to come together in the next step, don't worry!
Mix in flour, keep mixing until all comes together well.
Using a rubber spatula, gently fold in frozen or fresh blueberries.
Spread the mixture in the prepared dish and bake 25-30 minutes, or until it’s lightly golden brown on the edges and cool to a room temperature.
To make the lemon glaze, simply mix together powdered sugar, lemon juice, lemon zest and a splash of almond milk. You can refrigerate it around 10 minutes so that it hardens up.
Spread over blondies and let harden, about 10 minutes, before serving.