Preheat your oven to 350 degrees.
Line a muffin pan with liners or parchment paper & set aside.
In a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar together until light and fluffy, 3-4 minutes.
Beat in the eggs, one at a time, until well beaten.
Add the lemon juice, zest and vanilla and beat well again.
Stir in the flour and baking powder until well mixed. The dough should resemble a thick, sticky batter.
Evenly scoop the batter into the prepared muffin pan. A large spring-loaded scoop is probably your best bet.
If you want, sprinkle the top of each bun with pearl sugar.
Bake 22-27 minutes, until set, with lightly golden edges.
These are best enjoyed slightly warm or at room temp, on the day they're baked.