Preheat the oven to 350°F. Grease an 8x4-inch loaf pan with butter and dust it with flour. Set aside. In a medium-sized bowl, sift together the all-purpose flour, baking powder, and sea salt. Set aside.
In a large mixing bowl, use an electric mixer to cream together the softened butter, granulated sugar, and orange zest until light and fluffy. This process should take approximately 4 to 5 minutes.
Reduce the speed of the electric mixer to a low and add the eggs, one by one, beating well after each addition.
Then, add the buttermilk, orange juice, orange liqueur, and vanilla; continue to mix until incorporated.
Gradually add the sifted dry ingredients to the wet mixture, mixing well with a spatula or an electric mixer on low speed to get a nice, smooth mixture. Be careful not to overmix to maintain the cake's light texture.
Pour the batter into the greased loaf pan, spreading it evenly. Tap the pan gently on the counter to remove any air bubbles.
Bake in the preheated oven for 40 to 45 minutes or until a toothpick inserted into the center comes out clean.
Once the cake is baked and out of the oven, but it's still warm, use a toothpick or skewer to poke holes over the whole top surface. Slowly drizzle the fresh orange juice over the cake, then transfer the cake from the loaf pan to a wire rack to cool completely.