Simple Open Farmhouse-Style Vanity

Fasten a spacer block to each leg with glue and 2-1/2" screws. These build out the leg face so the aprons sit at the right depth for the top.

Fasten the side aprons to the spacers on both leg pairs, joining them into two end assemblies.

Fasten the top support to each end assembly. The front and back supports sit at different positions on the legs — the back one needs to sit flush with the back of the legs (and the wall behind it), both so the top registers correctly and so you have the option to screw the vanity to the wall through this apron for extra stability against two heavy sinks.

Fasten the front and back aprons between the two end assemblies, checking the whole frame for square before the glue sets.

Trace each sink's actual mounting template onto the top panel — don't guess a generic circle, above-mount basins vary in lip diameter and a hole cut to the wrong size either gaps or won't seat the sink. Cut with a jigsaw, then attach the top to the frame from underneath.

Sand everything, fill any visible screw holes, and finish with something rated for bathroom humidity — plain paint alone will fail near the sinks.