Heat the olive oil in a large, wide, heavy-bottomed pot over medium heat.
Add the onions and a generous pinch of kosher salt. Cook, stirring occasionally, until very soft and translucent, 8 to 10 minutes.
Add the garlic and Calabrian chiles. Cook about 2 minutes, stirring frequently, until fragrant.
Increase the heat to medium-high and add the tomato paste. Stir until fully combined with the onions, garlic and chiles.
Add the butter and another generous pinch of salt. Stir until the butter has completely melted into the tomato paste.
Cook the tomato paste, stirring and scraping every minute or two, until it is deep brick red, intensely caramelized, glossy and jammy. Let the paste make contact with the bottom of the pot so browned bits develop, then scrape them up. If the pot becomes truly dry, add another small drizzle of olive oil. Because this batch is much larger than a single recipe, go by color and texture rather than a set time.
Pour in the vodka and immediately scrape up all of the browned bits from the bottom of the pot.
Continue cooking until the sharp alcohol aroma has cooked off and the mixture returns to a very thick, concentrated, scoopable texture.
Taste and adjust with kosher salt. Let the concentrate cool completely.
Divide evenly among 6 freezer-safe containers or silicone molds. Freeze until solid, then transfer the portions to a freezer bag or airtight container if desired.