In a shallow pan such as a 8- or 9-inch pie pan, whisk to blend milk, eggs, brown sugar, cinnamon, and vanilla.
Rinse apple, core, and cut into 1/8-inch-thick slices. In a small bowl, mix apple slices with lemon juice.
In a 10- to 12-inch nonstick frying pan over medium-high heat, melt 1 tablespoon butter. Dip 1 bread slice at a time in milk mixture, turn over, and transfer to frying pan without crowding. Cook each batch, turning to brown both sides, about 6 minutes total. As done, set in a single layer on a 14- by 17-inch baking sheet and keep warm in a 200° oven. Add remaining butter to frying pan as needed to cook successive batches.
Meanwhile, in a small bowl, mix 1/3 cup maple syrup with yogurt.
Also, in a 1-cup glass measure, mix remaining 1/3 cup maple syrup and peanut butter. Heat in a microwave oven at full power (100%) until warm, about 30 seconds, stirring once or twice.
Place 2 slices of French toast on each plate. Drain apple slices and lay fruit equally onto toast; sprinkle with granola. Spoon maple-yogurt and peanut butter sauces equally onto portions.