Preheat your oven to 350°F. Prepare your bundt pan by spraying it generously with baking spray (the kind with flour in it). This is important — regular cooking spray will not work for a bundt cake. Trust me on this one. If you don't have baking spray, grease the pan with shortening or butter and dust it with flour, making sure you get into every ridge and curve.
Mix the cake batter. In a large bowl or the bowl of a stand mixer, combine the lemon cake mix, lemon pudding mix, eggs, oil, and the entire can of Sun Drop soda. Mix on low speed at first to bring everything together, then increase to medium and mix for about 2 minutes. You don't want to overmix — just until everything is well combined and smooth. If you don't have a mixer, a bowl and a spoon work just fine. This batter comes together easily either way.
Pour the batter into your prepared bundt pan. The batter will have a beautiful golden yellow color — you can already tell it's going to be a good cake just by looking at it. Smooth the top if needed.
Bake at 350°F for 35 to 40 minutes. Start checking around 35 minutes. The cake is done when it's golden brown on top and springs back when you lightly press it. You can also do the toothpick test — insert a toothpick into the center, and if it comes out clean, you're good. Every oven is a little different, so keep an eye on yours. If your oven runs hot like mine does, you may be closer to 35 minutes.
Let the cake cool in the pan for 10 minutes. Don't try to flip it out too early — give it those full 10 minutes. Then place your serving plate over the top of the pan and flip it over. The cake should release cleanly thanks to that baking spray.
Make the glaze while the cake cools in the pan. Whisk together the powdered sugar and lemon juice. You don't need to sift the powdered sugar — just keep stirring and any small lumps will work themselves out. Add just a small splash of water, a little at a time, until the glaze is thin enough to drizzle but not so runny that it slides right off the cake.
Glaze the cake while it's still warm. This is the key — glazing a warm cake allows the glaze to soak into the surface just a little bit, which adds flavor and moisture. Drizzle it over the top with a spoon and let it run down the ridges of the bundt naturally. It'll find its own way and look beautiful.
Let the glaze set, then slice and serve. The cake is delicious slightly warm, at room temperature, or even chilled the next day. It keeps well covered at room temperature for 2–3 days.