In a large mixing bowl, whisk together the warm water, instant yeast, and honey. Let it sit for about 5 minutes until it becomes frothy.
Add 3 1/2 cups of all-purpose flour and kosher salt to the yeast mixture. Stir with a wooden spoon until the dough begins to come together. Add more flour if too sticky.
Transfer the dough to a lightly floured surface and knead for about 5-7 minutes until smooth and elastic. Form into a ball and place in a greased bowl. Cover with plastic wrap and let rise for about 1 hour or until doubled in size.
While the dough is rising, prepare the filling by combining mascarpone cheese, fontina cheese, parmesan cheese, minced garlic, fresh thyme leaves, crushed red pepper flakes, thawed spinach, and chopped artichokes in a medium bowl. Mix well.
Once risen, punch down the dough and roll it out into a rectangle about 1/2 inch thick. Cut into approximately 3x3 inch squares.
Place a spoonful of filling in the center of each square. Fold the corners over the filling to create pockets. Arrange the squares standing up next to each other on a greased baking sheet.
Preheat oven to 375°F (190°C). Brush tops with melted butter and sprinkle coarse salt over them.
Bake for 25-30 minutes, or until golden brown and cheese is bubbly.
Let cool for a few minutes before serving. Pull apart and enjoy warm.