Preheat the oven to 375° F. Line your baking tray with parchment paper or grease it well. Sort your raspberries, if using frozen, thaw them completely.
First, make the crumbles: Combine flour, oats, and raw sugar in a bowl. Add the cold butter in small pieces and mix with your fingertips or the dough hook of a hand mixer until crumbly. Form the dough into a small ball, place in a bowl, cover and refrigerate until ready to use.
For the cake dough: Make sure all dough ingredients are at room temperature. In a large mixing bowl, beat the softened butter with the sugar and vanilla extract until creamy.
Add the eggs one at a time, beating each egg in before adding the next. Sift together the flour, salt and baking soda (or powder) and add to the butter mixture in batches. Stir until you have a smooth dough.
Fill the dough evenly onto the prepared baking tray. Spread the fresh raspberries on top. Be sure to drain the thawed raspberries well beforehand.Remove the crumble from the refrigerator and crumble evenly over the raspberries.
Bake the raspberry sheet cake in a preheated oven for about 30-35 minutes, until the crumbles are golden brown. Do the toothpick test by inserting a toothpick into the center of the cake. If it comes out clean, the cake is done. If there is still liquid dough on the top, bake for a few more minutes.
Remove the cake from the oven and let it cool on the baking sheet. Cut into even slices and serve with whipped cream or vanilla sauce.