Hydrogen generation via water electrolysis is of significant importance owing to its high efficiency, low cost, and sustainability. Herein, we propose a simple and low-cost technique for fabricating three-dimensional interconnected microporous carbon frameworks (MCFs) decorated with avalanches of microspheres for highly efficient hydrogen evolution reactions (HERs). The MCF electrode was fabricated via carbonization of a furan precursor, which was prepared by mixing a furan resin and table sugar. Although we aimed to develop a method for fabricating the MCF, we also discovered numerous accidental carbon microspheres on the sidewalls of the framework, which play a significant role in HER catalysis. We also confirmed the formation of microspheres at the interface between the furan resin and the sugar particles. The HER activity of the MCF electrode was evaluated in an alkaline solution and compared with that of commercially available nickel, nickel foam, and state-of-the-art Pt electrodes. The microporous carbon with a large pore size outperformed all electrodes except the Pt electrode, exhibiting a stable HER activity with an onset potential of 64 mV (vs. reversible hydrogen electrode (RHE)) and a current density of 10 mA/cm² at −143 mV (vs. RHE). The HER performance of the large pore size carbon electrode was superior to that of other heteroatom-doped carbon electrocatalysts and is compatible with that of metallic electrocatalysts. The superior HER performance of the large pore size carbon electrode can be attributed to the unique microspheres, which provide an abundance of active sites for efficient water splitting.