Combine flour, baking powder, & salt.
Cut butter cubes into the flour (either by pinching them between your fingertips or pulsing briefly in a food processor) until the butter resembles pea-sized lumps within the flour.
Add mushrooms, cheese, & parsley (if using).
In a separate bowl, beat together the eggs and cream.
Gently stir the egg mixture into the flour mixture until just combined.
Turn dough out onto a lightly floured surface, gently shape (I just used the heel of my hands) into a 10x10x1.5 inch square.
Cut into desired biscuit shape using 1-inch biscuit cutter or water glass with narrow rim.
Line a baking sheet with parchment paper or a silicone mat, place cut dough on sheet, and chill in freezer for at least 1 hour (from this point, can store frozen biscuit dough for 1 month in freezer).
Preheat the oven to 350°F. Remove biscuit rounds from freezer.
Once oven is pre-heated, bake biscuits until golden brown, about 30 minutes.