Preheat Oven: Grease a 10-12 cup Bundt cake pan. Preheat the over to 350℉.
Strawberry Puree: In a blender, puree the strawberries. Strain through a fine mesh strainer to remove any seeds.
Reduce Strawberries: Place strawberries in small pot and reduce over meduim low heat. Simmer the purée over low heat, stirring occasionally, until it thickens and reduces in volume. There should be about 1/2 cup of puree. Chill until ready to use.
Cream Butter and Sugar: Using a hand or stand mixer, cream together the butter and sugar until light and fluffy.
Add eggs and vanilla: Add eggs, egg yolk, and vanilla, beating well until the mixture is smooth and fully combined.
Add Salt and Baking Powder: Sprinkle baking power and salt over the batter and mix well.
Stir in Flour: Add the flour one cup at a time, mix on low until just absorbed.
Pour in milk: Add the milk and mix well. The batter will be thick.
Make Strawberry batter: Place half the batter in a bowl and set aside. Add in cooled strawberry puree and mix well.
Marble the Batter: Using a large cookie scoop or a 1/2 cup measuring cup, scoop the two batters into the prepared pan alternating the flavors.
Bake: Bake the cake at 350 for 50-60 minutes or a cake taster when inserted comes out clean. Cool the cake in the pan for 10 minutes and then remove the cake from the pan onto a cooling rack.