Preheat the oven to 350°F and line a cupcake pan with 24 cupcake liners.
In a large bowl, beat together the cake mix, sour cream, milk, oil, eggs, lemon juice, and zest until smooth (about 2 minutes).
Fill the liners 2/3 full and bake for 18–20 minutes or until a toothpick comes out clean.
In a small bowl, mix the juice and sugar. Heat it in the microwave in 30 second intervals until the sugar dissolves.
While the cupcakes are warm, brush them with the lemon syrup.
For the frosting, beat the butter until smooth. Add the powdered sugar a cup at a time and continue to mix. Then add the lemon juice and zest and mix. Add cream as needed, then the food coloring.
Pipe the frosting onto each cupcake and then top with a lemon slice or Mother’s Day topper.