Robotic prostheses can improve walking ability in persons with transfemoral amputations by closely matching kinetics and kinematics of the intact leg during walking. However, achieving this goal requires the prosthesis to adapt to walking speed, a function that no powered transfemoral prosthesis has yet achieved. In this paper, we present, and perform initial testing on a new control framework that allows biologically accurate leg function at varying walking speeds, without the need for tuning. The proposed framework comprises two novel controllers that rely on quasi-stiffness modulation in stance phase and minimum jerk trajectory in swing phase. Preliminary testing was conducted in an able-bodied subject using a bypass adapter to walk on a robotic prosthesis at five different walking speeds (from 0.62 to 1.16 m/s). Experimental results demonstrated the ability of the proposed controller to approximate intact leg function at different walking speeds.