Preheat your oven to 350℉. Grease a 10-cup bundt pan with melted butter and a light dusting of flour. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment (or use an electric hand mixer and large mixing bowl), beat butter and sugar on high speed for about 2 minutes, until fluffy. Then beat in vanilla and eggs, one at a time.
With mixer speed on low, beat in about one-half of the flour and all of the baking powder, mixing just until blended. Then add in milk and remaining flour and mix for one more minute, until there are no visible streaks of flour.
Using two separate bowls, split batter evenly.
Stir strawberry pudding powder into one bowl of batter until combined. Add cocoa powder and ½ cup milk in other bowl of batter, and stir to combine.
Pour both batters into prepared bundt pan, 1 cup at a time, alternating colors to give it a “messy marbled” or tie-dyed look.
Bake in preheated oven for 45-55 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Let the cake cool in the pan for 15 minutes before turning out on a wire cooling rack. Allow it to cool completely before adding strawberry icing.
Make icing by whisking powdered sugar, milk, and gel coloring together until blended. Drizzle over your cake and let it harden before serving.
Video
Notes
Use melted butter to grease the pan. The easiest way to get into the crevices of a bundt pan is to brush the butter on with a pastry brush.
Avoid over mixing the batter, which can cause the vanilla cake to be dry and crumbly. Stir just until there are no visible streaks of flour.
Wait at least 30 minutes before removing the cake from the pan. When bundt cakes are too warm, they can crumble when you try to remove them from the pan.
Is your cake dry? This is a very moist cake recipe, but if you have trouble with it, check out my tips on How To Make A Dry Cake Moist.