Mash the butter and salt together with a fork in a medium bowl. Add the coconut flour, almond flour, beaten egg, and xanthan gum and work with the fork until fully combined.Form the dough into a tight ball, wrap with plastic wrap and chill for at least ½ hour.Once chilled, place the ball of dough onto a piece of parchment paper. Cover with another piece of parchment (or wax paper) and roll into a 16 inch disk. Peel off the top layer of parchment paper carefully and place the disk and bottom parchment layer onto a cookie sheet.Combine the ricotta cheese, parsley, salt, pepper, and Parmesan cheese in a small bowl and mix thoroughly.Combine the olive oil, garlic, oregano, and salt in a small bowl.Preheat the oven to 375 degrees (F)Spread the ricotta layer over the raw crust, leaving a 2 inch border of crust with no ricotta.Top the ricotta layer with the cherry tomato halves, and then the prosciutto.Fold the 2 inches of the edge of the crust up over the sides of the filling.Drizzle the garlic oil over the top of the tart.Bake the tart in a 375 degree (F) oven for 35 minutes or until golden brown.Serve warm or chilled.