Make the cake. Preheat the oven to 170 C. Lightly grease a rectangular baking dish, 10x7 inch in size and set aside. I've in the past used an 8.5x6.5 inch dish for tres leches but found a larger one necessary here because the strawberry puree makes the soaking liquid runnier.
Make sure all your ingredients for the sponge are measured and kept ready. Sift the flour and salt (if using) and set aside. Melt the butter in the microwave or on the stove and set it aside to cool.
Now add a little water to a saucepan and bring it to a simmer over medium heat. While this is happening, combine the eggs, sugar and vanilla in a mixing bowl that fits neatly over the saucepan, without its base touching the water. Bring the heat down to low and place the bowl over the saucepan. Using a balloon whisk, whisk continuously for 5 to 7 minutes until the mixture is slightly warm, frothy and paler (see photos below). This double boiler step warms the eggs gently, creating more air and also helps dissolve the sugar so they beat better and become fluffy easily.
Pour this warm mixture into the bowl of a stand mixer fitted with the whisk attachment. Beat on high speed for about 5 minutes until the mixture has tripled in volume, thickened and leaves ribbons when you lift the whisk up (see photos below). I found the stand mixer bowl too large for a double boiler which is why I transfer the mixture after the above step, but if yours fits easily, you can just use the same bowl for both. You can also do this step with a hand mixer on high speed as long as your bowl is large and deep enough to hold the mixture as it increases in volume.
Now gently add half of the sifted flour to the bowl and fold it in using a silicone spatula. Do not mix vigorously, gently take your spatula to the bottom of the bowl, bring it up cutting through the airy batter and repeat. Add the remaining flour and do the same. While the batter will naturally deflate a little, don't worry about fully incorporating the flour as you fold. If a few streaks of it are visible, that's ok.
Slowly drizzle in the melted butter and once again fold gently but quickly to combine so that the butter doesn't settle at the bottom. Make sure your spatula goes right to the base of the bowl to get it all folded in.
Immediately pour the batter into the prepared pan and bake for 25 to 30 minutes until browned on top and when you press the surface lightly, it should spring back. A little over-mixing could cause the top to dome slightly and then fall as the cake cools. If this happens, don't worry, the texture of the cake isn't affected.
Let the cake cool completely in the pan at room temperature, at least 3 hours. Soaking the cake while it's still warm will make it soggy.
Make the tres leches mixture. Do this while the cake is cooling, so that the strawberry flavour is infused into the milks. Wash the strawberries and remove the stems. Slice in half and combine with one tablespoon sugar in a small bowl. Set aside for 15 minutes, then blend into a puree. Add to a bowl along with the condensed milk, evaporated milk and cream. Whisk thoroughly to combine and set aside at room temperature. If it's warm in your kitchen, place the tres leches liquid in the fridge and if it thickens by the time you're read to soak, add a little bit of plain milk or evaporated milk to thin it out so that it soaks easily. I did not find it necessary to strain the strawberry puree.
Run a knife around the edges of the cake to loosen it slightly from the pan, so that the liquid can soak in the sides too. Then poke multiple holes all over the cooled cake (still in the pan) with a fork, making sure you're poking it right to the bottom. Reserve 1/3 cup of the tres leches mixture from above, and gradually pour the rest over the cake, a few spoons at a time, waiting till it's almost fully absorbed before pouring more. By the time you've poured all of it, the liquid might pool on the edges and surface which is ok. See photos below.
Once done, cover the dish with clingfilm and refrigerate the cake at least overnight (it gets better the longer you chill it). By the morning, the liquid will have been fully absorbed. I find it soaks in about 1/3rd of the way, making the cake soft but not soggy, and also soaks in a bit on the bottom.
Make the compote. I do this the day I make and soak the cake, so the compote chills overnight as well and thickens, then the topping comes together in minutes the next day. Wash the strawberries, remove the stems and chop into small pieces. Add to a saucepan with one tablespoon sugar and one tablespoon water. Set it on low heat and stir constantly while the strawberries cook and come to a boil, mashing them gently to help them break down. Dissolve the cornflour in the remaining half tablespoon water in a small bowl and pour into the saucepan. Let the compote continue to cook and boil for 3 to 4 minutes until it thickens. Pour into a bowl, let it cool to room temperature, then refrigerate for at least 2 hours, preferably overnight.
Make the topping. Combine the chilled cream, sugar, vanilla and 1/4 cup compote in a mixing bowl. Beat on medium high speed with a hand mixer on until soft, rounded peaks form. The compote makes the cream a bit more loose, so beating to stiff peaks is difficult, this is ok. Transfer to the fridge to keep it chilled.
When ready to serve, spread the chilled cream all over the chilled cake. Decorate with the sliced strawberries. Refrigerate again for 20 minutes. Then slice into 6 large pieces and serve each with a little of the reserved tres leches mixture. This not only adds flavour but compensates for any parts of the cake that may have absorbed the liquid unevenly.
While this cake looks best the first two days since the strawberries will eventually bleed colour into the cream, it will continue to taste good for up to 5 days, refrigerated at all times. In fact, it gets more moist, and I love that, so I don't mind if the cream looks a bit splotchy with the pink colour from the berries :) Happy baking!