Preheat your oven to 350°F (175°C). Grease two 9-inch round cake pans and line the bottoms with parchment paper. Lightly dust with flour, tapping out the excess.

In a large bowl, beat the softened unsalted butter and granulated sugar together until light and fluffy (about 3-4 minutes on medium speed). This step helps incorporate air for a tender cake texture.

Beat in the eggs, one at a time, ensuring each is fully incorporated before adding the next. Add vanilla extract and mix until combined.

In a separate bowl, whisk together the flour, baking powder, and salt. Set aside.

Add the dry ingredients to the butter mixture in three additions, alternating with the milk. Begin and end with the dry mixture. Mix just until combined do not over mix.

Divide the batter evenly between the prepared pans. Smooth the tops with a spatula. Bake for 30–35 minutes or until a toothpick inserted in the center comes out clean. Cool the cakes in the pans for 10 minutes before transferring to a wire rack to cool completely.

In a small saucepan, heat the heavy cream until it just begins to simmer. Remove from heat and pour it over the chopped semisweet chocolate in a heatproof bowl. Let sit for 2–3 minutes, then whisk until smooth. Stir in salted butter, vanilla extract, confectioners’ sugar, and sea salt. Let the ganache cool and thicken slightly before spreading.

Place one cake layer on a serving plate or cake stand. Spread a layer of ganache on top. Place the second cake layer over it. Use the remaining ganache to frost the top and sides of the cake. Smooth with an offset spatula for a polished finish or create swirls for a rustic look.