Step 1: Preheat your oven to 325°F (165°C) and line a 10×15 inch jelly roll pan with parchment paper. Do not grease the sides as the cake needs to climb.
Step 2: In a large bowl, whisk together the egg yolks, 1/4 cup of granulated sugar, milk, oil, and vanilla extract until smooth and pale.
Step 3: Sift the cake flour and salt into the yolk mixture. Whisk gently until just combined, ensuring there are no large lumps.
Step 4: In a separate clean bowl, beat the egg whites with cream of tartar on medium speed until foamy. Gradually add the remaining 1/2 cup of sugar while continuing to beat until stiff, glossy peaks form.
Step 5: Gently fold the egg whites into the batter in three batches using a spatula. Be careful not to deflate the air bubbles, which are essential for this mini strawberry cream cake recipe.
Step 6: Spread the batter evenly into the prepared pan. Bake for 12-15 minutes or until the top springs back when lightly touched. Let the cake cool completely in the pan.
Step 7: Toss the sliced strawberries with a tablespoon of sugar and lemon juice; let them sit for 15 minutes. In the meantime, whip the heavy cream and powdered sugar until stiff peaks form.
Step 8: Use a 2.5-inch round cutter to cut circles out of the sponge. Place one circle down, pipe a ring of cream, fill the center with strawberries, and top with a second sponge circle. Finish with more cream and a whole berry.