Step 1: Prepare Your Pans
Preheat your oven to 350°F (175°C). Grease three 8-inch or 9-inch round cake pans with butter or non-stick spray. Line the bottoms with parchment paper circles and grease the paper too. This double insurance prevents any sticking disasters.

Step 2: Mix Dry Ingredients
In a large bowl, whisk together the flour, baking powder, baking soda, and salt. Set this aside – you’ll add it to the wet ingredients later.

Step 3: Cream Butter and Sugar
In your stand mixer bowl (or large bowl with hand mixer), beat the softened butter and sugar on medium-high speed for 4-5 minutes. The mixture should be light, fluffy, and almost white in color. This step incorporates air, which helps create a tender cake.

Step 4: Add Eggs and Vanilla
Reduce mixer speed to medium. Add eggs one at a time, beating well after each addition. Scrape down the bowl sides between additions. Mix in the vanilla extract.

Step 5: Alternate Dry and Wet
With mixer on low speed, add the flour mixture in three additions, alternating with the milk in two additions. Begin and end with flour. Mix each addition just until combined – overmixing develops gluten and makes cake tough. The batter should be smooth but don’t overwork it.

Step 6: Divide and Bake
Divide batter evenly among your three prepared pans (about 2½ cups per pan for 8-inch pans). Smooth the tops with a spatula. Tap pans gently on the counter to release air bubbles. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean and the cake springs back when lightly pressed.

Step 7: Cool Cakes
Let cakes cool in pans for 10 minutes, then carefully turn out onto wire racks. Remove parchment paper and let cool completely before assembling – this takes about 1 hour. Trying to frost warm cake is a recipe for melted frosting disaster!

Step 8: Make Dulce de Leche Soak
While cakes cool, whisk together ¾ cup dulce de leche and ¼ cup heavy cream in a small saucepan over low heat until smooth and pourable. Set aside to cool slightly.

Step 9: Make Buttercream
Beat butter in a large bowl on medium speed until creamy, about 2 minutes. Reduce speed to low and gradually add powdered sugar, one cup at a time. Add dulce de leche, 3 tablespoons heavy cream, vanilla, and salt. Increase speed to medium-high and beat for 3-4 minutes until light and fluffy. If frosting is too thick, add remaining tablespoon of cream.

Step 10: Level Cake Layers
If your cakes have domed tops, use a long serrated knife to carefully slice them off so layers stack evenly. Place first layer on your serving plate or cake stand.

Step 11: Soak and Fill
Brush the top of the first layer generously with dulce de leche soak. Spread about ¾ cup of buttercream on top, creating an even layer that goes all the way to the edges. Place second cake layer on top, press gently, and repeat the soaking and frosting process.

Step 12: Add Final Layer and Crumb Coat
Place the third layer on top (bottom-side up for a flat surface). Soak this layer too. Apply a thin layer of buttercream all over the cake – this is your “crumb coat” that seals in crumbs. Refrigerate for 20-30 minutes until firm.

Step 13: Final Frosting
Remove cake from fridge and apply remaining buttercream in a thicker, final coat. Use your offset spatula to create smooth sides and top, or leave it rustic if you prefer. A cake turntable makes this step much easier.

Step 14: Drizzle and Finish
Warm ½ cup dulce de leche in the microwave for 15-20 seconds until pourable but not hot. Drizzle over the top of the cake, letting it drip down the sides. If desired, sprinkle with a tiny bit of flaky sea salt for a sweet-salty contrast.

Step 15: Chill and Serve
Refrigerate cake for at least 30 minutes to set the frosting before slicing. Remove from fridge 15-20 minutes before serving for best flavor and texture. Use a sharp knife dipped in hot water (and wiped dry) for clean slices.