TKINTER, definierte Funktion wird nicht erkannt

import subprocess  # IMPORT FOR SUB PROCESS . RUN METHOD

POWERSHELL_PATH = "C:\\Windows\\system32\\WindowsPowerShell\\v1.0\\powershell.exe"  # POWERSHELL EXE PATH  
ps_script_path = "C:\\Users\\mr3968\\PycharmProjects\\SystemScriptWithGUI\\Powershell_Scripts\\browser.ps1"  # YOUR POWERSHELL FILE PATH  

class Utility:  # SHARED CLASS TO USE IN OUR PROJECT

    @staticmethod    # STATIC METHOD DEFINITION
    def openbrowser(script_path, *params):  # SCRIPT PATH = POWERSHELL SCRIPT PATH,  PARAM = POWERSHELL SCRIPT PARAMETERS ( IF ANY )

        commandline_options = [POWERSHELL_PATH, '-ExecutionPolicy', 'Unrestricted', ps_script_path]  # ADD POWERSHELL EXE AND EXECUTION POLICY TO COMMAND VARIABLE  
        for param in params:  # LOOP FOR EACH PARAMETER FROM ARRAY
            commandline_options.append("'" + param + "'")  # APPEND YOUR FOR POWERSHELL SCRIPT  

        process_result = subprocess.run(commandline_options, stdout = subprocess.PIPE, stderr = subprocess.PIPE, universal_newlines = True)  # CALL PROCESS

        print(process_result.returncode)  # PRINT RETURN CODE OF PROCESS  0 = SUCCESS, NON-ZERO = FAIL
        print(process_result.stdout)      # PRINT STANDARD OUTPUT FROM POWERSHELL
        print(process_result.stderr)      # PRINT STANDARD ERROR FROM POWERSHELL ( IF ANY OTHERWISE ITS NULL|NONE )

        if process_result.returncode == 0:  # COMPARING RESULT
            Message = "Success !"  
        else:
            Message = "Error Occurred !"  

        return Message  # RETURN MESSAGE

#ich lege hier einen neuen Reiter bzw. ein neues Button an

powershell_frame = ttk.Frame(notebook)
notebook.add(powershell_frame, text='Browser öffnen', underline=0)  
powershell_frame.columnconfigure(2, weight=1)
powershell_frame.rowconfigure(1, weight=1)

# button um die Funktion "openbrowser" aufzurufen. 

open_browser_btn = ttk.Button(
    powershell_frame,
    text='Öffne den browser'  
)
open_browser_btn.grid(sticky=tk.E, ipadx=5, ipady=5)

open_browser_btn.configure(command=lambda: Utility.openbrowser(POWERSHELL_PATH)) 

 File "C:\Users\mr3968\PycharmProjects\SystemScriptWithGUI\Istvan_TestApp\PowershellGUI.py", line 209, in <module>  
    open_browser_btn.configure(command=openbrowser)
NameError: name 'openbrowser' is not defined