In a small bowl, sift together flour, granulated sugar, baking powder and salt. Set aside.
In a larger bowl, mix together lemon juice, zest, milk, oil and egg.
Slowly add dry ingredients into wet ingredients. Mix until muffin batter forms.
Add a small drop of yellow gel food coloring into batter and mix until tinted (optional).
Scoop batter into each section of the muffin pan, filling it about 2/3 of the way.
In a separate bowl, mix all of the ingredients for the muffin topping - cut with a fork to create a “grainy” sugar topping.
Sprinkle the sugar muffin topping over each filled section of the pan.