Preheat the oven to 190C & grease & flour the base & sides of an 8-inch cast-iron skillet (or a cake pan). Set aside.
In a medium bowl, whisk together the flour, baking powder & bicarb. Set aside.
In a large bowl, beat together the butter & sugar until lighter in colour & fluffy. Beat in the egg & the egg yolk, mixing well between each addition. Finally, beat in the vanilla extract.
Add half of the flour mixture & beat on low until just combined. Add the buttermilk & beat again until just combined. Finally, add in the remaining flour & beat until just combined. Use a spatula to finish mixing altogether gently.
Spoon the batter into the prepared skillet & evenly spread out the top. Bake in the preheated oven for 30 minutes, or until golden brown all over & a skewer inserted into the centre comes out clean.
When the cake is cooling down, top with roasted strawberries. Serve in generous wedges!