How do you get the Fire Sprout Biscuit recipe?

You can't finish this alone. The 200 million total is shared by everyone on your server. Every participating player feeds the same server-wide track, and each node along the global community path hands out cosmetics to everyone on the way. The biscuit recipe sits at the very end. Your own play adds to the count, but the unlock arrives when the server gets there, not when you do.

Once the server reaches the last tier, go to the Event Vendor and open the item exchange menu. Fire Sprout Biscuits, also called flame cookies, appear in the supply shop under its trade or crafting option.

Don't confuse this with the personal track. The Sparkelf egg comes from 200 personal Spark points, which you earn on your own. The biscuit depends on the server's 200 million. The event lasts 81 days, so a server has the whole run to fill the global track.

What the biscuit does once you have it

Take a Fire Sprout Biscuit to a Bloom and use it to nurture the Bloom's ecosystem. That adds Sparkelves to the local spawn table as a catchable Aniimo, and a nurtured Bloom spawns its creatures in large numbers around it. One egg gets you a single Sparkelf. The biscuit gets you a whole patch of them to catch.