Preheat oven to 350 degrees. Generously coat large Bundt pan with shortening or nonstick spray.
In a large bowl, whisk together cake mix and dry pudding. Add water, oil, lemon zest, lemon juice, and eggs and stir to combine. Carefully fold in blueberries.
Pour into prepared pan and bake for 40 minutes or until a toothpick inserted comes out clean with a few crumbs attached.
Cool 15 minutes in pan. Invert on to a rack set over a baking sheet and cool completely.
To make the glaze, whisk together powdered sugar, water, and vanilla. Drizzle over cooled cake and let harden for at least 10 minutes.
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Notes
Boxed lemon cake mix: This gives you a head-start on the cake and is the secret to ultra-lemony flavor. Yes, even restaurants use boxed lemon cake mixes.
Instant lemon pudding mix: Add the dry pudding mix to the batter dry (you don't prepare the pudding separately). Even if your cake mix says "pudding in the mix," you should still add a box of instant pudding.
Lemon zest and juice: Zest the lemon before cutting it in half for juice.
Blueberries: Both fresh and frozen blueberries work here, just be sure to use only 6 ounces (not more). You don't need to thaw frozen blueberries; just toss them in frozen.
Yield: This Lemon Blueberry Cake makes 12 servings (or 9 if you like large slices).
Storage: Store covered at room temperature for up to 4 days.
Freezer: Wrap the unglazed cake in 2 layers of freezer-safe plastic wrap. Label, date, and freeze up to 3 months. Thaw at room temperature before glazing.