Preheat oven to 350°F.
In a large bowl, combine the yellow cake mix, vanilla pudding mix, oil, water, eggs, and vanilla. Beat with a mixer for 2 minutes.
In a separate small bowl, combine ½–¾ cup sugar with 1–2 tablespoons cinnamon.
Pour half of the cake batter into a 9x13-inch baking dish and spread evenly.
Sprinkle the cinnamon-sugar mixture evenly over the batter.
Pour the remaining batter over the cinnamon-sugar layer.
Using a knife, gently drag 5–6 lines through the batter in a crisscross pattern to create a swirl. Do not stir.
Bake for 35–40 minutes, or until the cake is baked through.
Let it cool slightly, slice, and enjoy! 😊
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