Preheat the oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan, or line it with parchment paper, leaving some overhang for easy removal.
In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy, using a hand mixer or stand mixer.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract until well combined.
In a separate bowl, sift together the all-purpose flour, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture, alternating with the milk. Begin and end with the dry ingredients, mixing until just combined after each addition. Be careful not to overmix.
Pour the batter into the prepared loaf pan, spreading it evenly with a spatula.
Place the loaf pan in the preheated oven and bake for 45 to 50 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely before slicing.
Once cooled, slice the butter cake into thick slices and serve.