Preheat your oven to 350°F (175°C). If making a cake, grease a 9x11 inch pan or two round pans. If making cupcakes, line a cupcake pan with liners. This helps prevent sticking and makes removal easy.

In a large mixing bowl, combine the lemon cake mix and lemon instant pudding mix. Mix thoroughly to ensure the pudding is evenly distributed, which helps the cake texture.

Add the sour cream, water, vegetable oil, and eggs to the bowl with the dry ingredients. Using an electric mixer on medium speed, mix for about two minutes until a thick batter forms. Scrape down the sides of the bowl as needed for even mixing. I like to use room temperature eggs for a smoother batter.

If making cupcakes, fill liners nearly full with the batter and bake at 350°F for 20 minutes. You should get about 24 full cupcakes. For cakes, pour the batter into your prepared pan(s) and bake for 25-30 minutes at 350°F. Avoid overbaking to keep the cake moist. Use a toothpick to test for doneness; it's done when the toothpick comes out clean. It's normal for cupcakes to sink slightly in the center after baking.

Place the very soft butter in a large mixing bowl. Add 4 cups of confectioners' sugar, the freshly squeezed lemon juice, and grated lemon peel. Beat until smooth and creamy. Gradually add the remaining sugar, one cup at a time, until the frosting is thick and spreadable. (You may only need 6 cups total.) I like my frosting extra tangy, so sometimes I'll add a touch more lemon juice.

Once the cake or cupcakes are completely cool, generously frost with the lemon frosting from Step 5. If your cupcakes have sunken centers, fill the indentations with more frosting. Serve at room temperature. For special occasions, I like to garnish with fresh berries right before serving!