In a large mixing bowl, add the butter and granulated sugar. Using an electric handheld mixer or a stand mixer, on medium-high speed, whisk for about 3-5 minutes until the mixture becomes creamy.
In a separate bowl, add one large egg, milk, and vanilla extract. Using a hand whisk, beat egg mixture until thoroughly combined.
Slowly add egg mixture to the whipped butter and sugar. Add little by little and whisk on medium speed until light and fluffy.
To prepare your dry ingredients, take a bowl or platter, sift flour, baking powder, baking soda, salt, and cinnamon and mix with a spatula.
Slowly add the dry ingredients and fold it in with the spatula until thoroughly combined. When you add all the dry ingredients, a dough will form. Use your hands to roll the dough until smooth.
At this point, place the dough in the refrigerator for at least 20-30 minutes. Chilling the dough will give you a firmer dough to work with that can be rolled out and shaped easily.
Once you are ready to work with your dough, preheat the oven to 350°F (177°C). Grease baking sheets (2 – 3) and line with parchment paper.
Once you remove the dough from the refrigerator, roll out the dough evenly (about 1/4-inch-thick) on a lightly floured surface. Alternately, you can roll it out between two large sheets of parchment paper. Then cut it into egg shapes or as you desire.
Place the cookies once cut to the desired shape in the lined baking sheets. Place each cookie on the baking sheet leaving a couple of inches around each cookie. Bake until very lightly browned on the edges, about 15 minutes.
Remove the cookies from the oven and allow them to cool on the baking sheet for about 5 minutes before transferring to a wire rack to cool completely.