Preheat oven to 350°F. Grease 10-cup Bundt pan with butter and, using a fine-mesh sieve, dust with cocoa, turning pan to coat crevices.
In bowl, whisk together all-purpose flour, rye flour, baking soda and salt.
In large bowl, whisk together olive oil, sugar and cocoa powder. Whisk in coffee, then add eggs 1 at a time, whisking well between additions.
Add flour mixture and whisk to combine. Stir with spatula to ensure no flour pockets remain. Add sour cream and vanilla, and whisk until batter is completely blended and smooth.
Scrape batter into prepared pan, smoothing top. Tap pan on countertop several times to remove any air bubbles. Bake on a baking sheet until cake tester inserted in centre comes out clean, about 40 minutes. Let cool in pan for 15 minutes; invert onto rack and remove pan. Let cool completely before transferring to cake plate.