Preheat oven and line pan:

Set oven to 350°F (175°C). Place paper liners in a 12-cup muffin pan.

Make lemon sugar:

In a large bowl, mix sugar and lemon zest. Rub together with fingers until aromatic.

Mix batter:

Beat butter and lemon-sugar mixture with an electric mixer on medium speed for 2-3 minutes. Add lemon extract and eggs one by one, beating well after each. Pour in buttermilk, then add flour, baking powder, and salt; mix until just combined, scraping bowl as needed.

Bake cupcakes:

Divide batter among prepared cups, filling each about ⅔ full. Bake for 15-18 minutes, until a toothpick inserted in center comes out clean. Let cool completely.

Core and fill with curd:

Using a paring knife, core each cupcake without cutting through the bottom. Fill cavities with lemon curd; optionally replace the cut-out tops.

Make frosting:

For frosting: Beat butter on medium-high speed until creamy. Add lemon extract and heavy cream; mix thoroughly. Slowly incorporate powdered sugar, beating for 1-2 minutes until smooth.

Tint and bag frostings:

Set aside ½ cup of frosting and tint with 2-3 drops yellow food coloring. Transfer to a piping bag fitted with a small round tip. Place the remaining vanilla frosting in another bag with a small round tip.

Pipe daisy decorations:

Pipe daisies: Starting at the edge of each cupcake, pipe inward with steady pressure to form 5-6 petals. Add a yellow dot in the center. Repeat for all cupcakes.

Store cupcakes:

Store covered at room temperature for up to 2-3 days.