heck/kubejs/server_scripts/recipes/essentials/stairs.js

// priority: 0

onEvent("recipes", event => {
  // For each stair crafting recipe that outputs 4x stairs, ...
  event.forEachRecipe({ id: /stairs/, type: "minecraft:crafting_shaped" }, recipe => {
    if (recipe.outputItems[0].getCount() != 4) return;

    let input  = recipe.inputItems[0];
    let output = recipe.outputItems[0].getId();

    // Quark limestone is disabled but some recipes still linger.
    if (/^quark:.*limestone.*$/.test(output)) return;

    // ... modify the output to return 6x instead of 4x.
    recipe.replaceOutput(output, "6x " + output, false, (out, orig) => out);

    // ... add a recipe to craft stairs in 2x2 crafting grid.
    event.shaped("3x " + output, [ "B ", "BB" ], { B: input });

    // ... add a back-crafting recipe to turn 1x stair => 1x block.
    event.shapeless(input, [ output ]);
  });
});