Step 1

First, make the strawberry jam. Clean the strawberries and cut them in small chunks. Add to a saucepan along with sugar, freshly squeezed lemon juice, and vanilla paste. Place the saucepan over medium heat, stir and cook for about 15 minutes or until the strawberries and soft and the mixture is thickened, stirring occasionally. Remove from the heat and leave to cool to room temperature.

Step 2

Make the brown butter. Place a saucepan with butter over medium heat. When the butter melts, continue to cook for 3 - 4 minutes or until it turns light brown and the beautiful nutty aroma appears. Remove from the heat, strain through a fine sieve into a bowl, and set aside to cool to room temperature. Preheat the oven to 180 °C / 350 °F or if you are using a fan-assisted oven, then preheat it to 165 °C / 330 °F. Prepare the baking sheet. Line a 25 cm x 35 cm (9 x 13-inch) baking sheet with parchment paper, then grease the paper with butter. Evenly dust with flour, then remove any excess flour from the pan.

Step 3

Sift the all-purpose flour into a small bowl. Using an electric mixer or a stand mixer, beat together sugar, eggs, vanilla paste, and salt until tripled in size and pale for about 6 - 8 minutes. Using a spatula, gently fold in the sifted flour until well combined. Add the cooled brown butter and a tablespoon of water. Stir to combine.

Step 4

Pour the sponge cake batter into the prepared baking sheet. Spread the mixture evenly using a spatula. Transfer to the preheated oven on the middle rack. Bake for 15 - 20 minutes at 180 °C / 350 °F or if you are using a fan-assisted oven, at 165 °C / 330 °F. The baked sponge cake should be golden brown and soft, make sure not to overbake it. Place a sheet of parchment paper over a damp towel. Dust the parchment paper with powdered sugar.

Step 5

Take the baked sponge cake out of the oven. Using a pairing knife gently scrape into the edges of the cake. Invert the cake onto the prepared parchment paper. Carefully remove the parchment paper. Using a serrated knife, make two shallow (2 - 3 mm or 5/64 inch) horizontal cuts 2 cm (1-inch) apart on the shorter side of the sponge cake near you. While the cake is still hot, roll into a swiss roll. Use the incision to help you make the first move and use the towel and parchment paper to help you roll the sponge tightly. Place on a wire rack and set aside for 30 minutes.

Step 6

Unroll the swiss roll. Spread the strawberry filling evenly over the surface, then roll tightly again and set aside (room temperature) for 15 - 30 minutes. Sprinkle with powdered sugar, slice into thick slices using a serrated knife and serve.