Preheat the oven to 350 F. Line a greased square metal pan, 8”x8 or 9”x9 with parchment paper (or use a brownie pan).
In the bowl of a stand mixer, beat together the butter, oil, sugar, salt, and lemon zest. While the mixer is running, add the vanilla and rose water. Let it beat for a full five minutes, until nice and fluffy. Add the eggs, one at a time and beat until well combined. Add the flour and baking powder and while the mixer is on low, drizzle in the kefir. Beat until batter is just smooth.
Dollop some of the cake batter into the bottom of the pan then spoon some of the strawberry reduction in and use an offset spatula (or butterknife) to swirl it in.
Dollop more cake batter and repeat. The idea is to layer and swirl the reduction into the cake batter. Make sure you have some sauce for the very top of the cake.
Bake for 40 minutes, or until the top springs back when poked (or a cake tester comes out clean). Let cool completely before frosting.