Preheat your oven to 350°F and grab a 9x13-inch baking pan. Lightly grease it with butter or cooking spray so the cake releases easily. This step takes two minutes but saves a lot of frustration later.

Combine the cake mix, melted butter, eggs, and milk in a large bowl. Mix everything together for about two minutes until you get a smooth batter. I've made the mistake of undermixing before—trust me, you want this really smooth.

Pour the batter into your prepared pan and spread it evenly across the bottom. Bake for 40 minutes until a toothpick inserted in the center comes out clean. The top should be golden brown when it's done.

While the cake bakes, prepare the pudding filling by whisking together the pudding mix, water, and 1/4 cup of milk. Set it aside for now so it can thicken slightly. This takes about three minutes of gentle whisking.

Remove the cake from the oven and let it cool for exactly five minutes—don't skip this. Using a fork, poke holes all over the top surface. I make these about every inch or so, creating a pattern across the whole cake.

Pour the pudding mixture slowly over the poked cake, letting it soak into those holes. Spread it evenly so it reaches all the edges. This is where the magic happens and your blueberry lemon poke cake family gets its signature moist texture.

Toss the fresh blueberries with the granulated sugar and lemon zest in a small bowl. Scatter them evenly across the pudding layer. Press them down gently so they stick.

Sprinkle the powdered sugar over the top as a final garnish, then refrigerate for at least two hours before serving. Cold cake always tastes better the next day, but if you're hungry now, one hour in the fridge works fine too.