Step 1: Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans or line with parchment paper. Set aside.
Step 2: In a medium bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt. Make sure there are no lumps.
Step 3: In a large bowl, cream together the softened unsalted butter and granulated sugar with an electric mixer until light and fluffy (about 2-3 minutes).
Step 4: Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Step 5: Gradually add the dry ingredients to the wet ingredients in three additions, alternating with the milk. Begin and end with the dry ingredients. Mix on low speed until just combined after each addition; do not overmix.
Step 6: Divide the batter evenly between the prepared cake pans. Smooth the tops with a spatula.
Step 7: Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs (not completely clean).
Step 8: Let the cakes cool in the pans for 10-15 minutes before inverting them onto a wire rack to cool completely. Do not frost until completely cool.
Step 9: To make the Vanilla Buttercream Frosting: In a large bowl, beat the softened butter until creamy. Gradually add the powdered sugar, 1 cup at a time, beating until smooth after each addition. Beat in the milk or cream, vanilla extract, and a pinch of salt until the frosting is light and fluffy.
Step 10: Once the cakes are completely cool, frost your classic vanilla cake as desired and enjoy!