This chocolate orange cake is citrusy, dense but also moist, and topped with the easiest cocoa powder glaze.
1. Preheat oven to 325 degrees if using a glass or dark non-stick loaf pan. If using a lighter metal pan, preheat to 350 degrees. Grease a 9x5 inch loaf pan with butter, then dust with flour, shaking out excess.
2. Add butter to large bowl and using a handheld or stand mixer, beat until creamy. Using a spatula, scrape down sides of bowl and add sugar. Beat until combined.
3. Add eggs and egg yolks, beating between each addition. Scrape down sides of bowl again, and mix on high briefly to ensure thoroughly combined.
4. Add juice of half an orange, vanilla extract, orange extract, and salt. Beat until just combined. Gradually add flour and cocoa powder, alternating and mixing between each addition, until just combined. Scrape down sides of bowl, add orange zest, and mix once more until evenly combined.
5. Pour into prepared loaf pan. Smooth top of batter with spatula. Transfer to oven and bake for 30 minutes, and then tent with foil and continue to bake for 20-25 additional minutes or until skewer inserted into thickest part comes out clean.
6. Meanwhile, combine powdered sugar, cocoa powder, and milk to make glaze. If the glaze is too thick, gradually add more milk, about 1 teaspoon at a time.
7. Remove loaf pan from oven. Let cool on wire rack, then run knife along edges of pan. Gently invert onto rack to cool completely.
8. Pour glaze over cake, top with halved orange slices, and sprinkle with thyme.