Put the strawberries and sugar in a heatproof container and microwave. Microwave until it has reduced to about 100 g, about 10 minutes at 700W.
When it has cooled down a bit, mash up the strawberries using a potato masher. Add the milk and mix well.
Add the B. ingredients to another heatproof bowl, and mix well with a whisk to make it fluffy. (Or sift them together.) Add the sauce from step 2 to this little by little, mixing well.
Microwave uncovered, about 1 minute 40 seconds at 700W. Add the egg white, mix very well, and microwave again, about a minute at 700W.
Mix well, and add the butter. Mix again until it dissolves, and knead well into a paste.
When it becomes shiny and thick and comes together in one lump as shown in the photo, it's done.
Wrap with plastic wrap and form into a 15 x 18cm rectangle, then freeze.
Story Behind this Recipe
Strawberries are affordable now, so I tried making this. It turned out sweet and sour and very fragrant - a luxurious strawberry sheet. It's my newest bread sheet, to fold into dough to make marbled bread and so on.
The strawberries weigh 200 g after being hulled. Please adjust the amount of sugar depending on the sweetness of the strawberries you are using. If you want to add a more sour flavor, add a little lemon juice. Please adjust the microwaving time depending on your microwave. Please refer to the directions for a detailed how-to.