Butter and flour two 9-inch cake pans. Line the bottoms with a round of parchment. Preheat the oven to 350°F.
Whisk the dry cake ingredients together in the bowl of a stand mixer.
Whisk together 3/4 cup Grenache Blanc, the olive oil, cream, eggs, and lemon zest in a medium bowl. When well blended, add to the dry ingredients and, using the paddle attachment, mix until the batter just comes together and all dry ingredients are moistened. Then, beat for an additional 30 seconds at medium-high speed.
Evenly divide the batter between the two cake pans and bake for 22-25 minutes. Let the cakes cool in the pans on a rack for 10 minutes.
While layers are cooling, make the glaze by mixing the remaining 1 cup Grenache Blanc with the butter and confectioners sugar in a large saucepan over medium heat. Bring to a simmer and cook until thickened slightly — about 2 minutes. You will have about 2 1/2 cups of glaze.
Using a skewer, poke holes all over the cakes and then slowly drizzle the glaze over the tops of the warm cakes, dividing it evenly between the two pans. Don’t try to drizzle it all at once; take your time. The cakes will eventually soak up all the delicious glaze.
Turn the cakes out of the pans onto serving platters or slice them directly from the pans. You can also freeze one of the cakes for future use!