The Vanguard Australian Shares Index ETF (ASX: VAS) is, by far, the most popular index fund on the ASX. As such, there will be more than a few ASX investors feeling pretty chuffed this Wednesday, as this index fund hits a new all-time record high.

Yep, VAS units started today's ASX session at $110.38. But soon after midday today, those units rose as high as $111.11 each. Before today, the Vanguard Australian Shares ETF had never had a price beginning with '$111', so it is indeed a momentous occasion for all VAS investors.

At present, this index fund has cooled off a little, but is still trading at $110.61 a unit, up 0.21% for the day thus far.

VAS ETF hits record ASX high

So how did we get here?

Well, the Vanguard Australian Shares ETF is an index fund that tracks the S&P/ASX 300 Index (ASX: XKO). This index reflects the performance of the 300 largest shares listed on the Australian stock market. That's everything from Commonwealth Bank of Australia (ASX: CBA) and Woolworths Group Ltd (ASX: WOW) to Ampol Ltd (ASX: ALD) and JB Hi-Fi Ltd (ASX: JBH).

Like most indexes, the ASX 300 is weighted according to market capitalisation, though. This means that the largest stocks in the ASX 300 have more impact on the index's performance than the smaller ones.

Because of this, we can thank the ASX's largest companies for today's new high. Indeed, we are seeing many of the ASX's biggest stocks making some momentous moves this session.

For instance, the big four ASX banks are all having a cracker.

National Australia Bank Ltd (ASX: NAB) has hit a ten-year high of $42.08 today, putting it up 12% year to date. Likewise, Westpac Banking Corp (ASX: WBC) has clocked a new 52-week high of $38.47 a share, the highest price we've seen since early 2015. ANZ Group Holdings Ltd (ASX: ANZ) is similarly at a new 52-week high of its own.

It's not just the banks, though. This Wednesday has seen Wesfarmers Ltd (ASX: WES), Origin Energy Ltd (ASX: ORG), Scentre Group (ASX: SCG), Lottery Corporation Ltd (ASX: TLC) and Seek Ltd (ASX: SEK) all hit new 52-week highs. Not to mention JB Hi-Fi.

So it's perhaps no wonder that the Vanguard Australian Shares ETF is following these leads by touching a new record high of its own today.

Vanguard Australian Shares Index ETF snapshot

This Wednesday's fresh new high for the ASX's VAS ETF caps off what has been a fantastic period for this popular index fund. As it currently stands, VAS units are now up 9.2% year to date, and up 11.8% over the past 12 months. That doesn't even include dividend returns, either.

Investors who were lucky enough to pick up units during the 'liberation day' sell-off in early April would be up more than 20% from those lows, too.

It will be interesting to see what's next for the Vanguard Australian Shares Index ETF.