Place a rack in the center of your oven and preheat the oven to 350 degrees F. Grease a 9x13-inch rectangular pan with butter, or butter and flour a 10-cup (9- or 10-inch) Bundt pan, tapping out the excess.

Place the beets in a high-powered blender or food processor with 1/2 cup sugar. Pulse a few times then blend into a puree (it will be a little grainy). Measure out 1 cup (there will be extra; save it to mix into a smoothie or even to flavor yogurt).

In a large mixing bowl, stir together the all-purpose flour, white whole wheat pastry flour, baking powder, and salt. In a separate large bowl, cream 8 tablespoons butter, Greek yogurt, and remaining 1 cup sugar on medium speed until creamy, pale yellow, and evenly blended, about 2 minutes. Add the eggs one at a time, beating until fully incorporated between each. Beat in the beet puree. The mixture will look curdled.

Add one-third of the flour mixture to the beet mixture. Beat on low speed just until the flour disappears. In turns, beat in half of the milk, then the next one-third of the flour mixture, then the second half of the milk, then the remaining flour mixture. Stir gently, just until the batter evens out.

Scrape the batter into the prepared pan and smooth the top. Bake just until the middle of the cake is set (your fingers will leave only a small indentation when you press the cake), 40 to 45 minutes (the time is the same whether you bake the cake in a sheet pan or a Bundt pan). While the cake bakes, prepare the rosé cake soak.

Let the baked cake cool 10 minutes, then pour half of the soak over the cake. Let sit at least 1 hour for the glaze to absorb. If using a Bundt pan, unmold it after 1 hour. If using a sheet pan, let cool completely in the pan.

When ready to serve, drizzle the remaining soak over the cake. Let sit a few minutes to set. Enjoy!