This fully configurable mod lets you craft slabs back into full blocks, allowing you to reuse slabs you no longer need. To do this, simply place two slabs on top of each other in the crafting table. If a crafting recipe already exists for stacking two slabs, you can instead craft the full block by placing two slabs side by side in the crafting grid.

Configuration

You can configure this mod directly in-game or by editing the JSON file located at config/slabstoblocks.json in your profile folder. Please note that any changes will require restarting Minecraft to take effect.

slabBlockList - List of strings specifying which slabs are converted into which blocks in this pattern: "slabname, blockname, pattern(not necessary)"

Few examples:

"minecraft:smooth_stone_slab, minecraft:smooth_stone",

"minecraft:cut_copper_slab, minecraft:cut_copper, -",

"minecraft:smooth_stone_slab, minecraft:smooth_stone, /",
This is a not part of the default config it is just an example of what you can do with it

Craft Slabs Back Into Blocks

another example