→ For Chocolate Thumbprints
                    
                      
                        01 - 
                        10 tablespoons (142g) unsalted butter, room temperature
                      
                    
                      
                        02 - 
                        ⅔ cup (140g) granulated sugar
                      
                    
                      
                        03 - 
                        1 large egg yolk (reserve white if rolling in nuts)
                      
                    
                      
                        04 - 
                        1 teaspoon vanilla extract
                      
                    
                      
                        05 - 
                        ¼ teaspoon pistachio extract (optional)
                      
                    
                      
                        06 - 
                        1¼ cups (156g) all-purpose flour
                      
                    
                      
                        07 - 
                        ⅓ cup (33g) dutch-processed cocoa powder, sifted
                      
                    
                      
                        08 - 
                        ½ teaspoon fine sea salt
                      
                    
                      
                        09 - 
                        ½ cup (60g) coarsely chopped pistachios (optional)
                      
                    
                  
                    → For Pistachio Cream Filling
                    
                      
                        10 - 
                        1.5 ounces (43g) white chocolate, chopped
                      
                    
                      
                        11 - 
                        3 tablespoons (48g) pistachio butter
                      
                    
                      
                        12 - 
                        2 teaspoons (4g) powdered sugar, sifted
                      
                    
                      
                        13 - 
                        ⅛ teaspoon fine sea salt
                      
                    
                      
                        14 - 
                        ⅛ teaspoon pistachio extract (optional)
                      
                    
                      
                        15 - 
                        ⅛ teaspoon vanilla powder (optional)