Preheat a large skillet or griddle on medium heat while you assemble your sandwiches.
Spread red pesto sauce on the inside of each slice of Artesano Brioche Bread.
On half of your bread slices, layer 1/4 cup of spinach leaves and two pieces of mozzarella cheese. Then, close the sandwiches with your other slices of bread.
Melt your butter in the skillet and cook the sandwiches on each side for about 3 minutes. Once the bread is golden and toasty and the cheese has melted, put the sandwiches on plates and cut in half. Enjoy warm!