Whisk the eggs, whole milk, vanilla extract, and ground cinnamon in a wide, shallow bowl until the ingredients are thoroughly blended into a smooth custard mixture.
Arrange four focaccia slices in the egg mixture. Allow them to absorb the custard for 3 minutes, then turn each piece over and soak the opposite side for another 3 minutes. Press the bread down lightly when necessary to encourage even absorption.
While the first batch is soaking, melt 2 tablespoons of the unsalted butter in a large nonstick skillet set over medium-low heat.
Place the four soaked focaccia slices in the heated skillet. Cook for approximately 2 to 3 minutes on each side, or until both surfaces are evenly browned and golden.
Transfer the cooked French toast to a wire rack. This allows excess steam to escape and helps preserve the exterior texture.
Soak the remaining four focaccia slices in the custard for 3 minutes per side, following the same process used for the first batch.
Melt the remaining 1 tablespoon of butter in the skillet. Cook the second batch for 2 to 3 minutes on each side until golden brown.
Serve the focaccia French toast while warm. Finish each portion with yogurt, fresh berries, and a generous drizzle of honey or syrup.