When you are making this ricotta toast it is best to use rye or dark wheat bread. The mushrooms and cheese can be a little heavy, so you need a bread that will not get soggy. Cutting the bread to at least 1/2" thickness helps that, as well as toasting it well before topping with the cheese. Rye bread gives a nice bitterness that pairs well with the mild ricotta and earthy mushrooms. Whole grain or wheat bread is often a bit sweeter, and more readily available, but works well with this topping. If you prefer, any of your favorite sandwich bread can work for this recipe. Just make sure it is toasted and sturdy enough to hold the toppings.