Preheat oven to 400°F.
Grease or line 12 standard muffin cups
Combine the flour, ¾ cup granulated sugar, zest of one lemon, baking powder, and baking soda, in a large mixing bowl.
In a microwave safe measuring cup, melt the butter by microwaving in 15 second intervals until melted.
Stir the milk into the melted butter with a fork, followed by the beaten egg, vanilla, and lemon juice.
Make a well in the center of the dry ingredients and pour the wet ingredients into the well. Using a rubber spatula, fold the dry ingredients and the went ingredients until just combined.
Reserve 12 whole blackberries, then very gently fold the remaining blackberries into the batter.
Using a medium ice cream/cookie scoop, evenly fill all 12 muffin wells, about 2/3 full. Top each well with a whole blackberry.
Bake for 14-18 minutes until the tops are golden brown and a toothpick inserted into the muffin comes out clean and dry.
While the muffins bake, combine the powdered sugar and lemon juice and remaining zest until a thick glaze is formed in a small bowl. The glaze should coat, but drip off of the back of a spoon. If your glaze is too thick, add more lemon juice or water 1 teaspoon at a time. If your glaze is to thin, add an additional tablespoon of powdered sugar until you reach the right consistency.
Once baked, cool the muffins for 10 minutes then transfer to a wire rack. Cool another 5-10 minutes before dipping the crowns of each muffin in the glaze. Allow the glaze to set, then dip a second time if desired. Cool completely and enjoy!