Marbled Jam Cake

Ingredients

• 1/3 cup oat flour (40g)
• 1/3 cup buckwheat flour (40g)
• 1/3 cup all-purpose flour (40g)
• 1 teaspoon baking powder
• 1/2 teaspoon baking soda
• 1/4 teaspoon salt (omit if you are using salted butter)
• 1/3 cup sugar (67g)
• large pinches grated nutmeg or spice of your choice
• 4 tablespoons unsalted butter, cold and cut into small cubes
• 1/4 cup quick oats (20g) or rolled oats (the latter will remain chewy in the completed cake)
• 1/2 cup plain yogurt (if you only have greek style, you'll need to increase the amount of milk)
• 1/8 to 1/4 cups whole milk (milk and yogurt can be interchanged, or replaced by buttermilk)
• 1 teaspoon vanilla extract (optional)
• 1/2 to 2/3 cups simple, runny, fruit-based jam or preserves, preferably with pieces of fruit