Preheat your oven to 350°F (175°C). Grease and flour three 8-inch round cake pans, or line with parchment paper.

In a large bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt. Set aside.

In a separate bowl, cream the softened unsalted butter until light and fluffy. Beat in the large eggs one at a time, then mix in the vanilla extract.

Gradually add the dry ingredients to the wet ingredients, alternating with the whole milk, beginning and ending with the dry ingredients. Mix until just combined, being careful not to overmix.

Divide the batter evenly among the prepared cake pans. Bake for 25-30 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cake layers cool in the pans for 10 minutes, then invert them onto a wire rack to cool completely before frosting.

In a large mixing bowl, beat the softened unsalted butter with an electric mixer until creamy and smooth, about 2-3 minutes.

Gradually add the sifted powdered sugar, one cup at a time, mixing on low speed until incorporated, then increasing to medium-high until fluffy.

Add the vanilla extract, heavy cream (or milk), and salt. Beat on high speed for another 2-3 minutes until the buttercream is light, fluffy, and smooth.

Once the cake layers are completely cool, use a serrated knife to level the tops of each cake layer if needed, creating a flat surface.

Place one cake layer on your serving plate or cake stand. Spread about 0.5 cup of buttercream evenly over the top.

Carefully place the second cake layer on top and spread another 0.5 cup of buttercream. Repeat with the third cake layer.

Apply a thin layer of buttercream all over the entire cake (top and sides). This is called a crumb coat, and it helps to trap any loose crumbs. Chill the cake in the refrigerator for 15-20 minutes to set the crumb coat.

Once the crumb coat is set, apply the remaining buttercream to the top and sides of the cake. Use an offset spatula or bench scraper to smooth the frosting for a neat finish.

Decorate as desired, or simply enjoy your beautifully baked layer cake!