biblatex: omit initials, display only lastname when citing single author

Question

I'm using biblatex with biber and want the following format for citing literature:

Lastname, Title

This is exactly what I get for Fielding.2000 (see below). My problem is that Mitchell.1997 is cited wrong. How can I omit these occurence of his initials?

Here is my example code:

\RequirePackage{filecontents}
\begin{filecontents*}{\literature.bib}
@book{Mitchell.1997,
author = {Mitchell, Tom M.},
year = {1997},
title = {Machine learning},
address = {New York NY u.a.},
publisher = {McGraw-Hill},
isbn = {0071154671},
series = {McGraw-Hill series in computer science : Artificial intelligence}
}

@phdthesis{Fielding.2000,
author = {Fielding, Roy Thomas},
year = {2000},
title = {Architectural Styles and the Design of Network-based Software Architectures},
url = {https://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm},
address = {Irvine},
urldate = {2018-01-01},
publisher = {Institude of Software Research},
school = {{University of California}},
type = {Dissertation}
}
\end{filecontents*}


\documentclass[ngerman]{article}
\usepackage{babel}
\usepackage{csquotes}


\usepackage[backend=biber,dashed=false,style=authortitle,maxbibnames=3,minbibnames=3,mincitenames=1,maxcitenames=3]{biblatex}
\usepackage{hyperref}
\addbibresource{\literature.bib}

\begin{document}
    \cite{Mitchell.2017} % T. M. Mitchell, Machine Learning
    \cite{Fielding.2000} % Fielding, "Architectural ..."

    \printbibliography % here, everything is allright
    \end{document}