Preheat the Oven:

1. Prepare your oven: Set your oven to 350°F (175°C) and allow it to preheat while you prepare the batter.
2. Line the muffin tin: Place cupcake liners in a 12-cup muffin tin to prevent sticking and to make the cupcakes easier to serve.

Prepare the Batter:

1. Cream butter and sugar: In a large mixing bowl, cream together the softened butter and granulated sugar. Use an electric mixer on medium speed to blend until the mixture is light, pale, and fluffy, about 3-5 minutes. Properly creaming the butter and sugar ensures a light cupcake texture.
2. Add eggs: Beat in the eggs one at a time, making sure to fully incorporate each egg before adding the next. This process helps to add structure and richness to the batter.
3. Incorporate lemon zest and juice: Stir in the freshly grated lemon zest and fresh lemon juice. This will give the cupcakes their bright, citrusy flavor.

Mix the Dry Ingredients:

1. Combine dry ingredients: In a separate medium bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and poppy seeds. Ensure the baking agents are evenly distributed to promote even rising during baking.

Combine Wet and Dry Ingredients:

1. Alternate dry ingredients and buttermilk: Gradually add the dry flour mixture to the wet butter mixture in three parts, alternating with the buttermilk. Begin and end with the dry ingredients, mixing just until combined after each addition. This method prevents overmixing, which can result in dense cupcakes.

Fill and Bake:

1. Fill cupcake liners: Use a spoon or ice cream scoop to divide the batter evenly among the cupcake liners, filling each about 2/3 full to allow room for rising.
2. Bake: Place the muffin tin in the preheated oven and bake for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean or with a few moist crumbs. Avoid overbaking to keep the cupcakes moist.
3. Cool: Remove the cupcakes from the oven and let them cool in the pan for 5 minutes. Then transfer them to a wire rack to cool completely before frosting.

Make the Frosting:

1. Cream the butter and cream cheese: In a medium mixing bowl, beat the softened cream cheese and butter together until smooth and creamy. Make sure there are no lumps.
2. Add sugar and lemon: Gradually add the powdered sugar, lemon juice, and lemon zest to the mixture. Continue to beat until the frosting is fluffy and well-combined.

Frost and Garnish:

1. Frost the cupcakes: Once the cupcakes are completely cool, use a spatula or piping bag to frost them with the lemon cream cheese frosting.
2. Garnish: Garnish with a thin slice of lemon and a sprinkle of poppy seeds for a decorative touch.