Converting a linq query or foreach loop into a form that is awaitable - linq

Question

I am trying to convert my method to Async. I cannot seem to grasp converting a linq query or foreach loop into a form that is awaitable. I read here on SO that EntityFramework + Linq don’t mix very well asynchronously. Perhaps that is why I could not find a previous Question that matches my needs exactly. Would someone care to point me in the right direction?
private static async Task<decimal> GetLastPriceAsync(string customer, string stockNumber)
{
Debug.WriteLine("Get Last Price Called");
decimal lastCost = 0;
var lastDate = new DateTime(1900, 1, 1);
if (string.IsNullOrEmpty(customer))
{
Debug.WriteLine("There was no customer");
return 0;
}
Debug.WriteLine("We have a customer");
if (string.IsNullOrEmpty(stockNumber))
{
Debug.WriteLine("There was no item");
return 0;
}
Debug.WriteLine("We have a Part Number");
try
{
IEnumerable<SA_HistoryHeader> orders =
DContext.SA_HistoryHeader.Local.Where(c => c.strCustomer == customer);
if (!orders.Any())
{
Debug.WriteLine("No order found.");
return 0;
}
Debug.WriteLine("We have previous Orders Found");
foreach (SA_HistoryHeader thisOrder in orders)
{
Debug.WriteLine("Looping through orders.");
DateTime date = lastDate;
IEnumerable<SA_HistoryDetail> details = thisOrder.SA_HistoryDetail
.Where(i => i.strStock == stockNumber && i.dteLineDate > date && i.bytLineType == 003);
foreach (
SA_HistoryDetail detail in
details.Where(detail => detail != null && !string.IsNullOrEmpty(detail.strDescription)))
{
if (detail.dteLineDate != null)
{
lastDate = (DateTime) detail.dteLineDate;
}
else
{
Debug.WriteLine("Order Date was null");
}
if (detail.curUnitPrice != null)
{
lastCost = (decimal) detail.curUnitPrice;
}
else
{
Debug.WriteLine("Last Cost was null");
}
}
}
}
catch (Exception ex)
{
Debug.WriteLine("Last Price Calc Error: " + ex.InnerException.Message);
}
return lastCost;
}