To make the crust, start by crushing pistachios in a food processor. Combine flour, salt, sugar, and pistachios (either in food processor or large bowl). Cut in butter until a coarse meal forms. Slowly add in water until dough comes together. Form into a disk and chill for 30 minutes.Pre-heat oven to 400°F. Line baking sheet with parchment paper. Melt 2 Tablespoons butter in large skillet; add leek rounds and cook until soft, approximately 3-4 minutes. Transfer to plate.In a small bowl, combine goat cheese, garlic, heavy cream, salt, and pepper.Remove galette dough from fridge and roll out on a floured surface. Roll into a 12 inch circle and place on parchment lined baking sheet. Spread goat cheese mixture over dough, leaving approximately 1 inch around the edges. Sprinkle rosemary on top of cheese mixture.Layer potato slices around goat cheese; drizzle with olive oil, salt, and pepper. Top with leeks. Fold edges over approximately 2 inches to create the galette. Brush edges with egg wash.Bake for 40-45 minutes, until edges are golden brown.