Preheat the oven to 350 degrees and grease a 9-inch square baking dish (or line it with parchment).
In a medium bowl, add the sugar and melted butter and stir to combine well.
Add the egg and vanilla and stir to combine.
Add the flour, baking powder, and salt, and beat with an electric mixture or stand mixer to combine.
Add the milk and beat again until the mixture is smooth with no lumps. Place the batter in the prepared pan.
Bake for 20-25 minutes, until the cake is lightly golden and springs back when lightly touched.
Remove from the oven and allow to cool at least 30 minutes before serving.
To serve, slice the cake into 9 pieces. Remove one piece from the pan and split it down the middle. Top half of the cake with strawberries and whipped cream, add the second half of cake, and top with more whipped cream and strawberries.
Serve right away.
Store any leftover cake covered at room temperature, separate from any leftover strawberries or whipped cream.
