Preheat oven to 350. Grease your loaf pan, set aside.
Melt butter, set aside to cool.
Mix flour, baking powder and salt in a medium bowl and set aside.
In a standmixer with the paddle attachment, or in a bowl to use with a hand mixer, combine sugar, eggs, lemon zest and lemon juice. Mix until well combined.
Add melted butter in small increments, mixing well between additions. You want to make sure to temper the eggs so the butter, if still warm, does not cook the eggs.
Add flour mixture and milk in two batches to the sugar mixture, adding flour then milk and mixing until well combined before adding more flour and milk.
Toss blueberries with 1 tbsp flour, gently fold into the batter.
Pour batter into prepared loaf pan.
In a bowl, combine crumb topping ingredients. Mix with your hands until a shaggy, crumbly mixture forms.
Top the batter (now in your loaf pan) with the crumb mixture.
Bake for ~65 minutes, turning the loaf half way through. I started checking mine at 55. It may need more or less depending on your oven. If the crumb starts to brown too quickly, pop a sheet of foil over it.