Ingredients - 1 Mortar, 3 cannon(culverin), 4 pike(noble), 2 sword (Highland
Noble), 6 archers(Noble Highland Archers), 3 cavalry(Borderhorse), 1 General.
Preferably a good command and morale general. Although the units in parenthesis are preferences, not a necessity. I rarely have all of my favorite toys together at once!

Location - Defending a River Crossings; Real estate is all about the location.
Take away the mongols mobility and make them play a game of scottish pokeman. More on the pokeman later.

Placement of units - Place your cannons on bluffs overlooking the river
crossing if possible. If not then place 2 cannons on the side of the river
crossing with the best field of fire and the other cannon on the other side
of the river crossing. Place 4 archers on the side of the river crossing that
would be facing the unshielded side of the attacking enemy. Place the other 2
archers on the other side of the crossing. Use the terrain to allow for direct
tiered fire on the river crossing when ever possible. Use the cavalry to
support the infantry. Place the infantry facing the river crossing as so -

sss sss
sss sss
sss sss
sss sss
pppp pppp pppp pppp
pppp pppp pppp pppp

Legend: p for pikeman, s for swordsmen

Battle strategy - As soon as the mongols are in range (probably immediately)
then open up on mongol rockets or trebuchets if any with the cannon. If those targets are not available then open up on the heaviest concentrations of troops for the paths of your cannonballs (enfilade), or fire on the heavy archer cavalry. From their you let the mongols come to you. They are the attacker, they will come to you. heh heh heh

Pikemen should be in shieldwall formation with guardmode on. I like 4 rows deep, you can use a deeper formation if you want to shorten the area in front of your infantry. In fact the first time I used this formation against the mongols, I only had a 2 pike unit frontage due to lack of pike available in that army. Counter attack the enemy directly in front of the pikemen once the pikemen have been engaged by single clicking on the enemy unit. Happy pokeman. Best done with the pike fix imho.

Use the cavalry to chase down the mongol stragglers after you have broken them on your pike wall. Border horse are fast, thats why I like them better for this job than knights

What are your winning strategies?