Step 1: Preheat your oven to 350°F (175°C) and grease and flour two 8-inch round cake pans. Line the bottoms with parchment paper for easy release.
Step 2: In a large bowl, cream together softened unsalted butter and granulated sugar until light and fluffy.
Step 3: Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next. Stir in vanilla extract.
Step 4: In a separate bowl, whisk together the cake flour, baking powder, and a pinch of salt. Gradually add the dry ingredients to the wet ingredients, alternating with milk, beginning and ending with the dry ingredients. Mix until just combined; do not overmix, as this can lead to a tough cake.
Step 5: Divide the batter evenly between the prepared cake pans. Bake for 25-30 minutes, or until a wooden skewer inserted into the center comes out clean. Let cool in the pans for 10 minutes before inverting onto a wire rack to cool completely.
Step 6: In a medium saucepan, whisk together milk, granulated sugar, cornstarch (or custard powder), and egg yolks until smooth. Ensure there are no lumps.
Step 7: Cook over medium heat, stirring constantly with a whisk, until the custard thickens and comes to a gentle boil. It should coat the back of a spoon.
Step 8: Remove from heat and stir in the remaining vanilla extract and butter until melted and smooth. Pour the custard into a bowl, cover directly with plastic wrap to prevent a skin from forming, and chill in the refrigerator for at least 2 hours, or until thoroughly cold and set.
Step 9: Once the cake layers are completely cool and the custard is chilled and firm, it's time to assemble your masterpiece. Level your cake layers if needed for a flat surface.
Step 10: Place one cake layer on your serving plate. Spread half of the chilled custard evenly over the top of the first cake layer, leaving a small border. Arrange a generous layer of sliced fresh strawberries over the custard.
Step 11: Carefully place the second cake layer on top. Spread the remaining custard evenly over this layer. Arrange the remaining sliced strawberries decoratively on top of the custard.
Step 12: For an extra touch of elegance, dust with powdered sugar just before serving. Chill the assembled cake for at least 30 minutes to allow the layers to set together before slicing.