In a medium bowl, combine granulated sugar, flour, and cold unsalted butter. Use a pastry cutter or your fingers to mix until the mixture forms a crumbly texture, resembling small peas. Once combined, refrigerate the crumb topping while you prepare the muffin batter.

Preheat your oven to 400°F (200°C) to ensure a perfect baking environment. Line a muffin tin with paper liners or grease it lightly to prevent sticking.

In a large mixing bowl, sift together the all-purpose flour, baking powder, and salt. Set aside your dry mixture.

In another bowl, cream together the softened unsalted butter and granulated sugar using an electric mixer for about 3 minutes until light and fluffy. Add in the lemon zest, pure vanilla extract, and lemon extract, blending well.

Add the whole egg and yolks to the butter-sugar mixture. Mix thoroughly until the eggs are well incorporated and the batter appears smooth.

Slowly add the dry ingredients to the wet mixture, alternating with the whole milk. Begin and end with the dry ingredients, mixing gently until just combined. Fold in the fresh lemon juice.

Spoon the muffin batter evenly into the prepared liners, filling each about two-thirds full. Sprinkle approximately 2 tablespoons of the chilled crumb topping over each muffin.

Place the muffin tin in the preheated oven and bake for 20-22 minutes, or until the tops are golden brown and a toothpick comes out clean.

Allow the muffins to cool in the tin for about 10 minutes. Once slightly cooled, transfer them to a wire rack to cool completely.

Whisk together confectioners' sugar, lemon extract, fresh lemon juice, and whole milk until smooth for the glaze. Adjust the milk for desired consistency.

Once the muffins are completely cooled, drizzle the lemon glaze over the tops using a spoon or piping bag.