Steps for Baking Lemon Cupcakes:

1. Begin by preheating your oven to 375°F (190°C). Prepare your cupcake tin by lining it with 12 cupcake liners.
2. Take a medium-sized bowl and sift together your all-purpose flour, baking powder, and kosher salt. Once sifted, set this bowl aside for later use.
3. In a larger bowl, cream the unsalted butter and granulated sugar using a hand mixer. Aim for a light and airy texture, which should take about 2 minutes.
4. Now, one at a time, add the eggs, ensuring each is fully incorporated into the mixture before adding the next. Follow this by stirring in the vanilla extract and lemon zest for a fragrant touch.
5. Gradually fold in about a third of your dry ingredients into the butter mixture. Alternate this with adding half of the milk and lemon juice. Continue this process, ending with the last portion of the flour mixture. Mix until just combined, taking care not to overbeat.
6. Fill each cupcake liner with the batter, about three-quarters full. Bake in the preheated oven for 15 to 17 minutes. Check for doneness with a toothpick inserted into the center of a cupcake—it should come out mostly clean. Let the cupcakes cool in the pan for 10 minutes before transferring them to a wire rack to cool completely.

Steps for Preparing Lemon Buttercream Frosting:

1. In a large mixing bowl, combine room temperature unsalted butter, lemon extract, and milk. Beat these together with a hand mixer on a medium setting until the mixture is smooth and well-combined. If you wish, add yellow food coloring to achieve your desired hue.
2. Gradually add the icing sugar to the butter mixture, beating at a low speed. Continue to add sugar until you reach your preferred frosting consistency.
3. Once the cupcakes are completely cool, use this lemon buttercream to frost them.