Radio-frequency　reflectometry　techniques　enable　high-bandwidth　readout　of　semiconductor　quantum　dots.　Careful　impedance　matching　of　the　resonant　circuit　is　required　to　achieve　high　sensitivity,　which,　however,　proves　challenging　at　cryogenic　temperatures.　Gallium　arsenide-based　voltage-tunable　capacitors,　so-called　varactor　diodes,　can　be　used　for　in　situ　tuning　of　the　circuit　impedance　but　deteriorate　and　fail　at　temperatures　below　10　K　and　in　magnetic　fields.　Here,　we　investigate　a　varactor　based　on　strontium　titanate　with　a　hyperabrupt　capacitance-voltage　characteristic,　i.e.,　a　capacitance　tunability　similar　to　the　best　gallium　arsenide-based　devices.　The　varactor　design　introduced　here　is　compact,　scalable,　and　easy　to　wire　bond,　with　an　accessible　capacitance　range　from　45　pF　to　3.2　pF.　We　tune　a　resonant　inductor-capacitor　circuit　to　perfect　impedance　matching　and　observe　robust　temperature-　and　field-independent　matching　down　to　11　mK　and　up　to　2　T　in-plane　field.　Finally,　we　perform　gate-dispersive　charge　sensing　on　a　germanium-silicon　core-shell　nanowire　hole　double　quantum　dot,　paving　the　way　toward　gate-based　single-shot　spin　readout.　Our　results　bring　small　magnetic　field-resilient　highly　tunable　varactors　to　mK　temperatures,　expanding　the　toolbox　of　cryo-radio-frequency　applications.　©　2023　American　Physical　Society.