Prepare the pan

Preheat oven to 350°F (175°C). Grease a 10-inch tube pan (or 12-cup bundt pan) generously with shortening, dust with flour, and tap out any excess.

Cream the butter

Place softened butter in a large mixing bowl. Beat with a stand mixer (or hand mixer) until smooth and creamy.

Add sugar

Scrape down the bowl, then add granulated sugar. Beat together for 1–2 minutes, until light and fluffy.

Mix eggs, yolks, and flavorings

In a separate bowl, whisk together the 6 eggs, 6 egg yolks, vanilla, and salt until yolks are broken and mixture is smooth.

Incorporate egg mixture

With mixer on low, slowly stream in the egg mixture. If you can’t pour in a steady stream, add in 5–6 parts, mixing well after each addition. Scrape the bowl, then beat on medium-high for 1–2 minutes until smooth.

Add flour

Reduce speed to low and gradually add the flour, about ¼ cup at a time, until fully incorporated. Scrape the bowl again and beat on medium speed for 1 more minute.

Fill pan & bake

Spread the thick batter evenly into the prepared pan, smoothing the top with a spatula. Bake on the center rack for 1 hour 10 minutes to 1 hour 15 minutes, or until a skewer inserted in the thickest part comes out clean or with a few moist crumbs. Do not overbake.

Cool & serve

Let cake cool in the pan for 20 minutes. Run a knife along the edges and center tube, then carefully invert onto a wire rack. Cool completely before slicing and serving.