✓ Preheat oven to 350°F / 175°C and place the heart-shaped silicone mold on a baking sheet

✓ Melt butter over low heat until light golden and nutty, then transfer to a mixing bowl

✓ Whisk sugar into melted butter until glossy and slightly pale

✓ Add egg whites one at a time, whisking until fully incorporated and batter becomes frothy

✓ Stir in vanilla extract

✓ Sift cake flour, all-purpose flour, baking powder, and salt together

✓ Gently fold dry ingredients into wet mixture until no streaks remain

✓ If making chocolate version, sift cocoa powder with flours and fold in

✓ Divide batter evenly among heart molds, filling each three-quarters full

✓ Tap baking sheet gently to release air pockets and level tops

✓ Bake for 12-14 minutes until edges turn deep golden brown and toothpick comes out clean

✓ Rotate sheet halfway through baking for even browning

✓ Remove from oven and let cakes sit in mold for 2 minutes

✓ Turn cakes out onto wire rack and let cool completely

✓ Optionally dust with powdered sugar or drizzle with melted chocolate before serving