In a medium bowl, combine all filling ingredients. Set aside for a moment.
Cake Batter
Preheat oven to 350F and adjust oven rack to middle. Line a 9×13 baking pan with parchment paper. Set aside.
In a large bowl with an electric beater or whisk, beat sugar and eggs well 1-2 minutes until eggs are slightly thickened. Beat in melted butter, yogurt, and vanilla until smooth.
In a separate medium bowl, combine flour, baking powder, and salt. Gently fold half of flour mixture into liquid with half of milk, then repeat with remaining flour mixture and milk until batter is smooth.
Scrape batter into prepared pan and smooth top. Spoon strawberry peach mixture evenly over top.
Streusel Topping
In small bowl, combine all topping ingredients until crumbly. Evenly sprinkle over strawberry peach filling.
Bake buckle at 350F 40-45 minutes until a toothpick inserted in middle comes out clean.
Cool buckle completely on a wire cooling rack, then slice into squares and serve. Enjoy!
Notes
Storing InstructionsCake may be stored in an airtight container on counter up to 4 days. Cake may also be frozen up to 1 month.