Start by preheating your oven to 350°F (175°C). This step is crucial for ensuring your bars bake evenly.
Line an 8x8 or 9x9 inch baking pan with parchment paper, leaving a bit of an overhang. This will make it easier to lift the bars out later.
In a large mixing bowl, combine the natural creamy peanut butter, honey, coconut sugar, vanilla kefir, egg yolk, and vanilla extract. Use a spatula or a whisk to mix until smooth and creamy.
In a separate bowl, whisk together the rolled oats, oat flour, powdered peanut butter, whey protein powder, baking soda, baking powder, and salt. Ensure everything is well combined.
Gradually add the dry ingredients to the wet mixture, stirring until just combined. Be careful not to overmix; you want a thick but cohesive batter.
Spread half of the oatmeal mixture into the prepared baking pan, pressing it down firmly to create an even layer. Then, spread the organic strawberry preserves over the top of this layer. Afterward, spoon the remaining oatmeal mixture on top and gently press it down again.
Place the pan in the preheated oven and bake for 25-30 minutes or until the edges are golden brown and a toothpick inserted into the center comes out clean.
Remove the bars from the oven and let them cool in the pan for about 10 minutes. Then, use the parchment paper overhang to lift them out onto a cutting board. Allow them to cool completely before slicing into squares or rectangles.
