They seemingly saved the best for last though and came away with a seven-try haul in an impressive display of running rugby on a fast, dry pitch, outside half Rhys Patchell adding 21 points with the boot.
Patchell was first on the score sheet with a penalty which was soon equalised by opposite number Jordan Wiliams. Cory Allen then scored the first try of the game with a short range effort under the posts which was improved by Glantaf School and CRICC pivot Patchell.
The Scarlets struck back instantly with No 8 Jonathan Williams powering over in the left hand corner to bring the score back to 10-8 but Blues wing Harry Robinson then ran over for a brace of well-worked tries, Patchell converting both to take their lead to 24-8.
It was an all-action first half with both sides able to cut through the opposition defence and Scarlets wing Aron Evans was next to score with a try converted by Jordan Williams but the Blues ended the half on a high with a touchdown for lock Ben Roach, the capital region going in 29-18 at the break.
There was no turning back for the Blues who came out after the break with the same intent and purpose as in the first half and scored 22 unanswered points until replacement wing Panashe Rushesha salvaged a consolation score for the West Wales region. Patchell had followed up an early penalty with a try for himself before lock Brad Thyer and replacement hooker Jac Hopkins touched down, with Patchell adding two conversions.
Blues head coach McIntosh said, "I'm chuffed to bits for the boys, especially to come away with such a convincing score. The Scarlets were slightly under strength and we certainly took advantage of that. Our attack was extremely accurate, we made a few errors in defence but the boys produced a superb performance with huge commitment and you can't ask more than that.
"It's a culmination of a whole season which has involved around 30 players and I just hope some of these players go all the way which is the ultimate aim."
Blues captain Ellis Jenkins added, "We had played the Scarlets twice earlier in the season and both times we thought we had the upper hand but we lost the first game and drew the second so it's great to win the match that counted most.
"We put into place what we had been practicing on the training pitch all year and for that type of rugby to come off in a final is very satisfying.
"We have grown a huge amount as a team and individuals this season, the aim now for all of us is to get into the Wales Under 18 set-up but we can't take anything for granted."