Preheat oven to 375°F (190°C). Line a 12-cup muffin tin with tall paper liners.
Make the crumb topping: In a bowl, whisk 1 cup flour, sugars, and salt. Add melted butter, mixing with a fork until small clumps form. Chill in the fridge.
For the muffin batter, take a bowl whisk 2 cups flour, baking powder, and salt.
Beat softened butter and sugar until light and fluffy (2-3 minutes). Add eggs one at a time, followed by vanilla and lemon zest.
Mix milk and lemon juice – it will curdle. Add dry ingredients alternately with the milk mixture, starting and ending with flour. Stir gently until combined.
Divide batter among muffin cups, about ¾ full. Break up chilled crumb topping and sprinkle generously on top, pressing lightly.
Bake for 20-22 minutes or until a toothpick comes out clean and tops are golden. Let cool for 5 minutes, then transfer to a wire rack.
For glaze, whisk powdered sugar and lemon juice until smooth. Drizzle over slightly warm muffins. Enjoy!